Between 2004 and 2020 we collected multiple specimens of two undescribed species of snail-suckers in the states of Guerrero and Oaxaca, Mexico. Additionally, we collected other species of snail-suckers from across Mexico to serve as comparative material. Currently, thirteen species of snail-suckers are known from Mexico. These thirteen species are distributed among three genera: four are currently assigned to Sibon, two to Dipsas and seven to Tropidodipsas. Tropidodipsas fasciata and T. sartorii have two subspecies each in Mexico and T. fischeri has two subspecies, one of which occurs in Mexico. Of these, we sampled three of the four species of Sibon known from Mexico, both species of Dipsas and five out of the seven species of Tropidodipsas. We were not able to sample Tropidodipsas repleta Smith, Lemos-Espinal, Hartman & Chiszar, 2005; T. zweifeli Liner & Wilson, 1970; the subspecies T. fasciata kidderi; T. sartorii macdougalli; Sibon linearis Pérez-Higareda, López-Luna & Smith 2002; nor the population of T. cf. philippii from Oaxaca reported by Kofron (1987). Additionally, we sampled four species of Geophis which belong to two species groups that are hypothesized to be closely related to snail-suckers (Sheehy 2013).

We photographed all live snakes, including dorsal, lateral, and ventral profiles, and euthanized them with pentobarbital. We took tissue samples from muscle or liver upon death and preserved them in 96% ethanol. We fixed specimens in 10% formalin and transferred them to 70% ethanol for permanent storage.

The material collected was deposited at the Instituto de Investigaciones sobre los Recursos Naturales (INIRENA) of the Universidad Michoacana de San Nicolás de Hidalgo (UMSNH) in Morelia, Mexico; the Museo de Zoología, Facultad de Ciencias (MZFC) of the Universidad Nacional Autónoma de México (UNAM) in Mexico City; the Colección Herpetológica de la Facultad de Ciencias Biológicas (CHFCB) of the Universidad Juárez del Estado de Durango (UJED) and the University of Texas at Arlington, Texas (UTA). Although we formally accessioned the specimens we collected, several specimens examined from both the MZFC and UTA collections have not been catalogued, in which case we list the original field numbers and the respective museum in which they were deposited. Original field number abbreviations are as follows: CIG (Christoph I. Grünwald) to be catalogued at MZFC; ENS (Eric N. Smith) to be catalogued at UTA; JAC (Jonathan A. Campbell) to be catalogued at UTA; JRV (Jacobo Reyes-Velasco) to be catalogued at UTA.

Museum acronyms throughout follow Sabaj-Pérez (2016). Representative specimens of snail-suckers and Geophis were examined in the following collections, in addition to specimens deposited in the collections reported above: the University of Kansas Natural History Collection (KU), Natural History Museum of Los Angeles County (LACM), Texas Cooperative Wildlife Collection (TCWC), University of Illinois Museum of Natural History (UIMNH). Specimen numbers for all material examined are provided in Appendix 1. We were not able to measure type specimens of some previously described taxa, so we used the measurements of the type specimens provided in the original descriptions and other published literature.

Our measurements and character states follow Kofron (1980) for all Dipsadidae and Downs (1967) for Geophis. Measurements and character states were taken from data published in Kofron’s succession of work on Mexican Dipsadidae such as Tropidodipsas Kofron (1980), Dipsas gaigeae and D. brevifacies (Kofron 1982), T. fischeri species group (Kofron 1985a), Tropidodipsas (Kofron 1987), T. sartorii species group (Kofron 1988), S. dimidiatus (Kofron 1990) as well as Davis (1953) for T. guerreroensis. Some measurements and characters for Central and South American Dipsadidae were taken from Lotzkat et al. (2012) and Arteaga et al. (2018). Abbreviations used in the text and tables are as follows: snout–vent length (SVL), tail length (TL), total length (TotL), head length (HL), head width (HW), snout length (SL), eye diameter (ED), chinshield (CS).

Scale counts were performed with the aid of a dissecting microscope. Measurements were taken with a ruler or digital calipers (Truper®, Mexico) under a dissecting microscope. Bilateral characters were scored on both left and right sides and given in that order, separated by a slash (/). Head length was measured from the tip of the snout to the posterior end of the parietals (following Peters 1964), head width was measured at the widest point of the head at the posterior part of the jaw. All scale dimensions were measured at their maximum.

To examine dentition characters, the maxilla and ectopterygoid were removed from the skull and cleansed in a dilute solution of Proteinase K for approximately one hour.

We sequenced genetic data from two nuclear (DNAH3, NT3) and two mitochondrial (cytb, ND4) loci, and combined our data with previous studies of the group (Arteaga et al. 2018; Sheehy 2013).

We used 370 µL of Monarch gDNA Tissue Lysis buffer (New England Biolabs T3011L) and 20 µL of Proteinase K (New England Biolabs P8107S) to digest the tissue at 55°C overnight. We extracted whole genomic DNA from lysed samples using the Serapure bead extraction protocol of Rohland and Reich (2012) with modifications based on Glenn et al. (2019) for Sera-Mag SpeedBeads (Fisher Scientific 09-981-123).

We used polymerase chain reaction (PCR) to amplify two nuclear genes and two mitochondrial genes. The nuclear genes were DNAH3 using DNAH3_f1 as the forward primer and DNAH3_r6 as the reverse primer (Townsend et al. 2008) and NT3 using NT3_F3 as the forward primer and NT3_R4 as the reverse primer (Noonan and Chippindale 2006). The mitochondrial genes were cytb using Gludg-L as the forward primer (Palumbi 1996) and ATRCB3 as the reverse primer (Harvey et al. 2000) and ND4 using ND4 as the forward primer and ND4_Leu as the reverse primer (Arevalo et al. 1994). All four loci were amplified using a standard PCR protocol: 95°C for 3 min 30 sec, 35 cycles of 95°C for 30 sec, 51°C for DNAH3 and NT3 and 53°C for cytb and ND4 for 30 sec, 72°C for 1 min, followed by 15 min at 72°C and a final hold at 10°C. All PCR reactions were 30 µL and contained the following: 16.9 µL of water, 3 µL of 10X Reaction Buffer (New England Biolabs M0320L), 1.8 µL MgCl₂ (25mM), 0.6 µL dNTPs (2.5mM each; New England Biolabs N0446S), 0.3 µL DMSO, 0.6 µL of each primer (10 µM), 0.2 µL of Taq DNA Polymerase (New England Biolabs M0320L), and 6 µL of genomic DNA. PCR reactions were purified using 5 µL of Quick Cip (New England Biolabs M0525S) and incubating at 37°C for 30 min and inactivating the enzymes at 80°C for 15 min.

Sequencing was done in both directions using Eurofins Genomics LLC (Louisville, KY, USA). Forward and reverse reads were merged and trimmed in Geneious Prime v2020.2.1 (Biomatters Ltd., Auckland, NZ) and manually screened for errors and ambiguities. Heterozygous sites in nuclear genes were coded using International Union of Pure and Applied Chemistry (IUPAC) ambiguity codes. All sequences were deposited in GenBank. Information on all the new sequences as well as other sequences used in this study are found in Table 1.

Alignments for each locus were performed in MAFFT version 7 (Katoh & Standley 2013). We used Geneious v9.1.6 (Biomatters Ltd, Auckland, NZ) to manually trim any regions of poor alignment and to make sure that protein-coding genes were in the correct reading frame. We then concatenated all genes with the use of FASconCAT-G v1.04 (Kück and Longo 2014). Our concatenated dataset consisted of 3,248 bp, of which 1987 bp correspond to two mitochondrial loci and 1261 bp to two nuclear loci.

We chose the best-fit model of nucleotide evolution for each locus with the use of the Bayesian Information Criterion (BIC) in PartitionFinder v1.1.1 (Lanfear et al. 2012). Table 2 shows the best-fit model for each locus. We partitioned our dataset by locus and by codon position. We then performed Bayesian phylogenetic inference (BI) in Mr. Bayes v3.2.2 (Ronquist et al. 2012) on the CIPRES science gateway server (Miller et al. 2011).

Our Bayesian phylogenetic analysis consisted of four runs of 10 million generations, sampling every 1,000^th generation. Each run contained four chains, three heated and one cold. We checked for convergence between runs with the use of Tracer v1.6 (Rambaut et al. 2015) by visually inspecting overlap in likelihood and parameter estimates between runs, as well as effective sample sizes and potential scale reduction factor (PSRF) for each run. The individual runs had converged by 200,000 generations (based on the PSRF), so we conservatively discarded the first 25% of each run as burn-in. The runs were combined with the use of TreeAnnotator (Bouckaert et al. 2019) and visualized in FigTree v1.4.2 (Rambaut 2014). We consider a clade as highly supported if the posterior support value was greater than 0.95.

Additionally, we calculated uncorrected p-distances for the mitochondrial gene Cytochrome B (cytb) in the program MEGA X (Kumar et al. 2018). We calculated genetic distances of cytb once we completed the concatenated data set.

We used a total of 79 individuals in our molecular phylogeny, including 76 snail-sucker individuals as well as three outgroup taxa. Of the individuals used, 18 specimens were novel sequences obtained by us, representing 9 taxa. As shown by previous studies (Sheehy 2013; Arteaga et al. 2018), the three currently recognized genera of snail-suckers form a monophyletic group, which also received high support in our analysis (Posterior Probability [pp] = 1) (Fig. 6).

Our results recovered a monophyletic Dipsas, including members previously allocated to Sibynomorphus, a South American genus previously synonymized with Dipsas (Arteaga et al. 2018). The only exception was D. gaigeae, a species restricted to western Mexico. This species and Tropidodipsas fischeri each formed monophyletic, highly supported, independent clades but their relationships with the remaining species of snail-suckers are poorly supported and remain ambiguous as they form a polytomy in a clade containing Tropidodipsas, Sibon and Geophis. Combined, these results were consistent with those reported by Sheehy (2013). We also recovered a strongly supported clade containing the majority of species of Tropidodipsas. This clade consisted of two main groups. The first one included both taxa from southern Mexico described herein, as well as an individual of T. cf. fasciata from Yucatan (with low node support, pp = 0.67). The other group in Tropidodipsas consisted of an individual of T. cf. fasciata from Tamaulipas (Fig. 7A), T. fasciata from Oaxaca, which was sister to T. guerreroensis + T. philippii (also with low node support, pp = 0.65). The fact that the three geographically distinct populations of T. fasciata fall in different positions in the tree suggest that this taxon needs further study and better sampling. Unfortunately, more material is currently unavailable, as most T. fasciata samples are from the Oaxaca (Isthmus of Tehuantepec) population. The type locality of T. fasciata has not been delimited beyond “Mexico” and thus it would be difficult to assign a specific clade to that name. Our suggestion is that a more detailed study of the T. fasciata species complex should be undertaken in the future.

The remaining snail-suckers grouped into two clades. The first clade is composed of multiple species currently allocated to three different genera: Sibon sanniolus from southeastern Mexico; the species Tropidodipsas annulifera and T. sartorii; multiple members of the genus Geophis. This clade had moderate support (pp = 0.88) and the node with T. sartorii and T. annulifera plus several Geophis was recovered with more robust support (pp = 0.93). From here on we refer to all these species as Geophis (see below). Several of the internal nodes were recovered as weakly supported (pp < 0.90). These results are similar to what was presented by Sheehy (2013) and Arteaga et al. (2018).

The last clade consisted of the majority of species in the genus Sibon, with the exception of S. sanniolus. The majority of nodes in this clade were recovered as highly supported (pp > 0.95). These results were in agreement with Sheehy (2013).

Our phylogenetic results support the novelty of the two species described herein, as we show that they are not conspecific with any previously described taxa and form monophyletic clades. Furthermore, our results suggest that these two new species are each other’s closest relative, and together with a sample of T. cf. fasciata from Yucatan they form a sister clade to the clade containing T. cf. fasciata, T. philippi and T. guerreroensis. Our analysis supports the validity of T. guerreroensis as a species as originally described, not a subspecies of T. fasciata, as it is more closely related to T. philippi and a sample of T. cf. fasciata from Tamaulipas (CIG 819) than the T. fasciata from nearby Oaxaca (see below).

Our molecular analyses confirm the results of Sheehy (2013) that some species previously included in Tropidodipsas and Sibon (T. annulifera, T. sartorii and S. sanniolus) are actually more closely related to members of the genus Geophis than to other snail-suckers. However, we disagree with Sheehy’s (2013) recommendation that new genera should be erected for each of these species. Instead, we consider it more appropriate for taxonomic stability to regard these three species as members of the genus Geophis, with the following new combinations: Tropidodipsas annulifera Boulenger 1894 = Geophis annuliferus comb. nov. (Boulenger, 1894); Tropidodipsas sartorii Cope 1863 = Geophis sartorii comb. nov. (Cope 1863); and Sibon sanniolus (Cope 1866) = Geophis sanniolus comb. nov. (Cope 1866). We refrain from assigning the two species of the Tropidodipsas sartorii species group (sensu Kofron 1988; Smith et al. 2005) for which we do not have genetic material (T. repleta and T. zweifeli) to Geophis, and provisionally retain them in Tropidodipsas, although it has been suggested by previous authors that a close phylogenetic relationship between these taxa is likely (e.g., Kofron 1988). It should be noted that synonyms of both G. annuliferus comb. nov. and G. sartorii comb. nov. have previously been described in the genus Geophis. Geophis tecpanecus Dugès 1896 was synonymized with G. annuliferus comb. nov. by Scott (1967) and Geophis annulatus Peters 1870 was synonymized with G. sartorii comb. nov. by Boulenger (1894).

Figure 6. 

Bayesian phylogenetic inference of members of the Dipsadidae based on two mitochondrial loci and two nuclear loci. All nodes with support of less than 0.5 are collapsed, while those with posterior support equal to 1 are marked with a black dot. New species described here in bold.

As revised here, the genus Tropidodipsas thus comprises eight species: Tropidodipsas fasciata Günther 1858, T. fischeri (Boulenger, 1894), T. guerreroensis Taylor, 1939 (see comment below), T. papavericola sp. nov., T. philippii (Jan, 1863), T. repleta Smith, Lemos-Espinal, Hartman & Chiszar, 2005, T. tricolor sp. nov. and T. zweifeli Liner & Wilson, 1970. The two species described herein are each other’s closest relative and comprise a clade together with samples assigned to T. fasciata from the Yucatán Peninsula (Fig. 7B). These two species together with T. philippi, T. guerreroensis, and the various populations assigned to T. fasciata form a species group that we continue to recognize as the T. fasciata species group (Kofron 1987, Wallach 1995). The phylogenetic relationships of Tropidodipsas repleta and T. zweifeli are unknown as no genetic data currently exist for these species. With the removal of Geophis annuliferus new comb. and G. sartorii new comb. these two species become unassignable to a species group. Genetic material of these two species is needed to determine whether their relationship is indeed with Tropidodipsas, or whether they should also be placed in Geophis. The generic affinities of Dipsas gaigae (Oliver, 1937) and Tropidodipsas fischeri (Boulenger, 1894) are not clear as they render their respective genera paraphyletic, and these two species probably deserve their own monotypic genera as suggested by previous authors (Kofron 1985b; Fernandes 1995; Sheehy 2013). However, this is beyond the scope of this paper and we provisionally retain them in their respective genera.

Tropidodipsas guerreroensis was described by Taylor (1939) as a member of the genus Tropidodipsas that he considered closely related to T. fasciata. Later, Álvarez del Toro and Smith (1956) relegated it to a subspecies of T. fasciata, an arrangement followed by Kofron (1980, 1987). Mertz et al. (2010) reported a specimen (UTADC 3701 = JRV-31) purportedly of this form from western Guerrero as a range extension of T. fasciata (Fig. 7C), as that journal did not accept the use of subspecies at the time. Sheehy (2013) included this specimen in his study, along with a second specimen (JAC 27750) from the vicinity of Hwy.134 in western Guerrero. He mistakenly referred to this specimen as T. philippii. In his phylogenetic analysis he also included a third specimen from the vicinity of Candelaria Loxicha, Oaxaca (JAC 24267), which he labeled as a potential undescribed species.

We included all three of these specimens in our analyses, along with a specimen from central Guerrero (INIRENA 2781) collected relatively near the type locality of T. guerreroensis (<90 km) that fits the original description very well (Fig. 7D). Our samples encompass the currently known distribution of the species, ranging from western Guerrero east to near Candelaria Loxicha in the south-central portion of the Sierra Madre del Sur of Oaxaca. The genetic distances of the mitochondrial gene cytb between the westernmost specimens of T. guerreroensis on Hwy. 134 in Guerrero and the easternmost specimen from near Candelaria Loxicha in Oaxaca is less than 6%, suggesting that all four specimens belong to one cohesive lineage, albeit with considerable intraspecific divergence, probably the result of isolation-by-distance.

In contrast, the easternmost individual of T. guerreroensis (Candelaria Loxicha, Oaxaca) has a genetic distance of 12.4–12.5% compared to nearby T. fasciata from various localities in the Isthmus of Tehuantepec, Oaxaca (Fig. 8A, B). For comparison, the western population of T. guerreroensis (Hwy. 134, Guerrero) has a genetic distance of 6.9–8.5% from the nearest sampled T. philippii in Michoacán, which suggests a closer relationship to T. philippii than to T. fasciata, as shown by our phylogenetic analyses, or recent gene flow. Thus, we suggest that T. guerreroensis represents a diagnosable, monophyletic species that is closest related to T. philippii.

These results show that among Mexican snail-suckers inter-population intra-specific genetic distances of the cytb mitochondrial gene range from 3–7%, whereas inter-specific genetic distances of closely related species (such as T. philippii, T. guerreroensis, and T. fasciata) range between 7–10% and other species have genetic distances >10%. It is notable that in our results intraspecific distances of cytb are less than 0.7% in T. papavericola sp. nov., less than 0.4% in T. fasciata, but 3–6% in T. guerreroensis.

Kofron (1980) described a specimen (LACM 104321) from the Sierra Madre del Sur of Oaxaca as “Sibon sp. cf. philippii”. He apparently considered the specimen to be of enough significance that he provided a detailed description, including scalation and color pattern, and even gave comparisons of how it differed from other Tropidodipsas philippii. He also recognized the uniqueness of the habitat compared to that of other T. philippii, but he refrained from designating a name for this form. Later, Kofron (1987) included this specimen, along with three others from Oaxaca (KU 137655, UCM 49372, UIMNH 73681) in his “Sibon philippii” (=Tropidodipsas philippii). He did not give any further explanation as to why he placed these specimens in T. philippii, and the scale counts and ranges given by him for T. philippii include these specimens.

Figure 7. 

Closely related species of Tropidodipsas from southern Mexico. Tropidodipsas cf. fasciata from Municipio de Ocampo, Tamaulipas (A); Tropidodipsas cf. fasciata from Municipio de Merida, Yucatan (B); Tropidodipsas guerreroensis from Municipio de José Azueta, Guerrero (C); Tropidodipsas guerreroensis from Municipio de Atoyac de Álvarez, Guerrero (D).

It is important to note that these southern specimens are over 750 km from the nearest populations of T. philippii in Michoacán, and originate from elevations between 1600–2100 m a.s.l., whereas T. philippii is known from elevations usually below 1500 m a.s.l. We have reviewed detailed photographs of three of these specimens (LACM 104321, KU 13766, UCM 49372) and it is likely that these high-elevation populations are referable to T. papavericola sp. nov. or represent an undescribed species, closely related to it. We were not able to examine the other specimen (UIMNH 73681) from southern Oaxaca due to institution closures related to the Covid-19 pandemic. Unfortunately, genetic material is not available for the high-elevation populations of Tropidodipsas from the Sierra Madre del Sur of Oaxaca. Future collecting is necessary to properly assign these populations to a species.

Sheehy (2013) included a specimen of Geophis sartorii new comb. (JAC 30401) purportedly from the vicinity of El Tuito, Jalisco, in his phylogenetic analyses. Geophis sartorii new comb. is restricted to eastern Mexico, so a specimen of this species from Jalisco greatly increased the known range of the species. The sample did indeed group with G. sartorii new comb. in Sheehy’s genetic analysis and not with the superficially similar G. annuliferus comb. nov., which is known from that region of Jalisco. We inquired about this specimen at the UTA collection and were informed that it was collected by Mr. Paulino Ponce-Campos. We contacted Mr. Ponce-Campos about the provenance of this specimen, and he told us that he specifically remembers providing the UTA field crew with a specimen of G. sartorii new comb. that he had collected in the state of San Luis Potosí and given them while they were in Jalisco.

Figure 8. 

Closely related species of Tropidodipsas from southern Mexico. Tropidodipsas fasciata from Municipio de Santo Domingo Zanatepec, Oaxaca (A–B); Tropidodipsas philippii from Municipio de Minatitlán, Colima (C–D).

Considering that Sheehy (2013) does not list any Geophis sartorii new comb. as coming from San Luis Potosí, we suggest it is very likely that this is the correct provenance of JAC 30401 and the locality listed by Sheehy (2013) was confused with another specimen with origins in Jalisco. This is further supported by the fact that the genetic distances of a fragment of the mitochondrial gene cytb between JAC 30401 and two G. sartorii new comb. (INIRENA 12783–84) which we collected in San Luis Potosí is 0.0. We have included this specimen (JAC 30401) as “locality unknown” and strongly doubt that G. sartorii new comb. is present in the state of Jalisco. However, Geophis sartorii macdougalli new comb. was recently reported from the Pacific versant of Guerrero by Blancas-Hernández et al. (2019). It would be interesting to verify the identity of this Guerreran population with molecular tools and assess how it is related to populations of G. sartorii new comb. on the Atlantic versant of Mexico and around the Isthmus of Tehuantepec. If the Guerrero population indeed belongs to G. sartorii new comb., then the presence of additional populations of G. sartorii new comb. on the Pacific versant of Mexico can be expected.

The species of Tropidodipsas described above are the two species with the smallest known range in the genus, and likely are also the two species needing the most conservation attention. Tropidodipsas papavericola sp. nov. can be considered micro-endemic. It is known from only one biogeographical formation (#48 – Guerreran Sierra Madre del Sur Mixed Temperate Woodland) as defined by Grünwald et al. (2015). While it is currently known from four distinct localities, all fall within this biogeographical formation or right at its lowermost limit. Widespread illegal logging is present at two of the localities (pers. obs.) and illicit poppy farming is present at or near all four localities. As poppy prices drop due to international supply and demand, and competition from synthetic drugs such as fentanyl, illicit poppy farmers tend to fluctuate to other businesses. This often leads to illegal logging (pers. obs.) and thus widespread habitat destruction. We suggest that this new species be awarded the highest conservation category possible by the Mexican government, and that studies are undertaken to determine its vulnerability to the habitat destruction caused by illegal logging. Also, further sampling should focus on southern Oaxaca to determine whether populations from the Sierra Madre del Sur above San Gabriel Mixtepéc are assignable to this species.

Figure 9. 

Similar looking but not closely related snail-suckers from southern Mexico. Sibon nebulatus from Municipio de Ixtlahuacán, Colima (A); Sibon nebulatus from Municipio de Las Margaritas, Chiapas (B); Tropidodipsas fischeri from Municipio de Rayón, Chiapas (C); Tropidodipsas fischeri from Municipio de Unión Juárez, Chiapas (D).

Figure 10. 

Distribution map of species in the Tropidodipsas fasciata species group in Mexico. Triangles represent type localities, type localities are only mapped when known with certainty.

Tropidodipsas tricolor sp. nov. is apparently widely distributed along the windward slopes of the Sierra Madre del Sur of Guerrero and Oaxaca. It has been collected in three biogeographical formations (#12 – Guerreran Tropical Dry Forest & Savanna; #48 – Guerreran Sierra Madre del Sur Mixed Temperate Woodland; #49 – Malinaltepec - Putla Sierra Madre del Sur Mixed Temperate Woodland) as defined by Grünwald et al. (2015). The type locality experiences small-time agricultural disturbance and some logging, but for now seems to be free of any major threats to the persistence of the habitat. The two localities in the Sierra Madre de Guerrero, near el Pazclar (Municipality of Leonardo Bravo) and near La Cienega (Municipality of Malinaltepec), are threatened by logging, but it does not appear as widespread as is the case with T. papavericola sp. nov. The only known locality of T. tricolor sp. nov. in Oaxaca is threatened by deforestation for small-scale agriculture. We did not see signs of illegal logging or drug cultivation in this area, however in general the habitat in this area is more disturbed than in the vicinity of the type locality.

The Environmental Vulnerability Score (EVS) was developed by Wilson and McCranie (1992) for use with amphibians in Honduras. The EVS system was later applied to the amphibians and reptiles of Mexico by Wilson et al. (2013). It was further modified by Porras et al. (2013) to better apply to animals outside of Honduras. Grünwald et al. (2015) applied the EVS system as modified by Porras et al. (2013) and defined Biogeographical Formations specific to reptiles and amphibians for the country of Mexico. These more-inclusive Biogeographical Formations replaced the “Forest Formations” initially outlined by Wilson and McCranie (1992) in their application to Honduras. Herein we apply the EVS system as outlined by Porras et al. (2013) and Grünwald et al. (2015) to the Tropidodipsas fasciata species group as defined above.

T. fasciata 3 + 3 + 4 = 10

T. guerreroensis 4 + 6 + 4 = 14

T. papavericola sp. nov. 4 + 8 + 4 = 16

T. philippii 3 + 7 + 4 = 14

T. tricolor sp. nov. 4 + 6 + 5 = 15

The IUCN categories for assigning conservation status are the most commonly used scheme to assess the degree of extinction risk for taxa at the species level (Porras et al. 2013). The criteria used for this assessment are stipulated in the Guidelines for Using IUCN Red List Categories and Criteria (Version 8.1; August 2010). We evaluate the species of the T. fasciata species group (as defined herein) below:

T. fasciata = Least Concern

T. guerreroensis = Least Concern

T. papavericola sp. nov. = Near Threatened

T. philippii = Least Concern

T. tricolor sp. nov. = Least Concern

Our evaluation of T. papavericola sp. nov. as near threatened is based on the limited extent of its known distribution. While known from more localities than just the type locality, all known localities fall within a 90 km radius of the type locality in the same physiographic province. This fact, coupled with the moderate habitat destruction for small scale agriculture present at all collecting localities, supports our evaluation of this species as “near threatened”.

Dipsas brevifacies.— Mexico: Yucatan • 36.4 km S of Valladolid on Hwy. 295, Municipio de Tixcacalcupul, 25 m a.s.l., INIRENA 2791, CIG 1841 • 1.4 km E of fair complex on Calle 253, Merida, Municipio de Merida, 11 m a.s.l., INIRENA 2792, CIG 1844.

Dipsas gaigeae.— Mexico: Colima • 3.0 km N of Ixtlahuacán Rd. on Hwy. 54 frontage road, Municipio de Tecomán, 322 m a.s.l., JAC 28327 • 6.4 km N of Ixtlahuacán Rd. on Hwy. 54 frontage road, Municipio de Tecomán, 494 m a.s.l., JAC 28587 • Guerrero: 10.8 km N of Hwy. 200 on Hwy. 134, Municipio de Jose Azueta, 130 m a.s.l., JRV 0030.

Geophis annuliferus comb. nov.— Mexico: Colima • El Mixcuate, on Colima–Minatitlán Road, Municipio de Villa de Álvarez, 569 m a.s.l., JAC 30142 • Guerrero: 24.1 km NE of Hwy. 200 on Hwy. 134, Municipio de José Azueta, 330 m a.s.l. JAC 27792.

Geophis bicolor.— Mexico: Colima • 10 km (airline) NNW of Quesería, Municipio de Cuauhtémoc, 2128 m a.s.l., INIRENA 2795–97, CIG 1786–88 • Jalisco: 3 km (airline) NNW of Cumbre de Guadalupe, Municipio de Talpa de Allende, 2095 m a.s.l., INIRENA 2793–94, CIG 1576–77 • 9.2 km SW of Tapalpa on road to San Gabriel, Municipio de Tapalpa, 2012 m a.s.l., INIRENA 2808, CIG 1850 • Plan de Cervantes, on Valle de Juárez – Santa María del Oro Rd., Municipio de Quitupan, 2291 m a.s.l. INIRENA 2809, CIG 1851 • Michoacán: 3.2 km NW of Apo, Municipio de Tancítaro, 2010 m a.s.l., JAC 24684.

Geophis nigrocinctus.— Mexico: Jalisco • Cerro Tetilla, 20.1 km (airline) W of Talpa de Allende, Municipio de Talpa de Allende, 2466 m a.s.l., JAC 30704 • Michoacán: Between Paso Malo and Rancho Las Torrecillas, on Coalcomán-Dos Aguas Rd., Municipio de Coalcomán de Vázquez-Pallares, 2115 m a.s.l., CIG 0568.

Geophis omiltemanus.— Mexico: Guerrero • Omiltemi, Municipio de Chilpancingo de los Bravo, 2115 m a.s.l., ENS 11496.

Geophis sanniolus comb. nov.— Mexico: Yucatan • 2.2 km E of Homún on road to Huhi, Municipio de Homún, 16 m a.s.l., INIRENA 2790, CIG 1842 • 12.7 km S of Hwy. 180 on road to Tahdzibichén, Municipio de Yaxcabá, 30 m a.s.l., JAC 24409 • 2.8 km S of Tixcacalcupul on Hwy. 295, Municipio de Tixcacalcupul, 26 m a.s.l., INIRENA 2789, CIG 1839.

Geophis sartorii comb. nov.— Mexico: San Luis Potosí • 1.1 km SW of Huichihuayan, on road to El Nacimiento, Municipio de Huehuetlán, 90 m a.s.l., INIRENA 2784, CIG 1758 • 2.0 km NE of Xilitla on Hwy. 120, Municipio de Xilitla, 552 m a.s.l., INIRENA 2785, CIG 1759 • 2.2 km NE of Xilitla on road to El Túnel, Municipio de Xilitla, 679 m a.s.l., INIRENA 2783, CIG 1518 • Yucatan: 6.7 km S of Tixcacalcupul on Hwy. 295, Municipio de Tixcacalcupul, 26 m a.s.l., INIRENA 2786, CIG 1840 • Unknown: JAC 30401.

Geophis tarascae.— Mexico: Colima • 7 km (airline) NNW of Montitlán, Municipio de Cuahutémoc, 1846 m a.s.l., INIRENA 2807, CIG 1631 • Jalisco: 1.9 km S of El Montoso, Municipio de Quitupan, 1969 m a.s.l., INIRENA 2806, CIG 1372 • Michoacán: 2.5 km S of southern edge of Uruapan, on Hwy. 37 libre toward Lombardia, Municipio de Uruapan, 1563 m a.s.l., JAC 24692.

Sibon nebulatus.— Mexico: Chiapas • 0.8 km SW of Ejido Morelos, Municipio de Huixtla, 1185 m a.s.l. INIRENA 2788, CIG 0788 • Colima: Road from Comala to Minatitlán, 739 m a.s.l., JAC 30102 • Hwy. 54 frontage road, near La Salada, 301 m a.s.l., JAC 30124 • Michoacán: 9.4 km NNW of Caleta de Campos, Municipio de Aquila, 15 m a.s.l., INIRENA 2787, CIG 1481.

Tropidodipsas fasciata.— Mexico: Chiapas • 13.5 km (airline) NW of Rizo de Oro, Municipio de Cintalapa, elev. unknown, JAC 22920 • Oaxaca: 33.6 km SSE Matias Romero, Municipio de Asunción Ixaltepec, LACM 103765 • 17.3 km W of Zanatepec, Municipio de Santiago Niltepec, 56 m a.s.l., LACM 38212 • 3.2 km N of Tehuantepec, Municipio de Santo Domingo Tehuantepec, 32 m a.s.l., LACM 114067 • 60.8 km WNW of Tehuantepec on Hwy. 190, Municipio de Magdalena Tequisistlán, LACM 74042 • 51.2 km NW of Magdalena Tequisistlán turnoff on Hwy. 190 to Oaxaca, Municipio de Nejapa de Madero, LACM 38211 • 2.9 km W of Hwy. 195 on road to Almoloyas, Municipio de El Barrio de la Soledad, 270 m a.s.l., JAC 30740.

Tropidodipsas sp. cf. fasciata— Mexico: Tamaulipas • Gómez-Farías Rd., at the Ojo de Agua turnoff, Municipio de Gómez Farías, 243 m a.s.l., CIG 0819 • Yucatan: 15.4 km NW of Hunucmá on road to Sisal, Municipio de Hunucmá, 5 m a.s.l., INIRENA 2780, CIG 1843.

Tropidodipsas fischeri.— Mexico: Chiapas • Selva Negra, Municipio de Rayón, 1895 m a.s.l., CHFCB-0352 • Chichihuites, Municipio de Unión Juárez, 2090 m a.s.l., CHFCB-0332, 0335.

Tropidodipsas guerreroensis.— Mexico: Guerrero: Acahuizotla, 853 m a.s.l., KU 61242, TCWC 7477–80 • 1.6 km W Acahuizotla, 853 m a.s.l., TCWC 7481–82 • 2.8 km SW of Rincón de la Parotas, on Atoyac de Álvarez to Puerto del Gallo Rd., Municipio de Atoyac de Álvarez, 273 m a.s.l., INIRENA 2781, CIG 1857 • Oaxaca: 12 km S of Candelaria Loxicha on Hwy. 175, Municipio de Candelaria Loxicha, 291 m a.s.l., JAC 24267 • 1.6 km SE of Cacahuatepec, Municipio de San Juan Cacahuatepec, 360 m a.s.l., UIMNH 52958.

Tropidodipsas papavericola sp. nov.— Mexico: Guerrero • 12.5 km S of Puerto del Gallo on road from Nuevo Dehli to Puerto del Gallo, Municipio de Atoyac de Álvarez, 1914 m a.s.l., INIRENA 2801, CIG 1495 • 18.1 km S of Puerto del Gallo on road from Nuevo Dehli to Puerto del Gallo, Municipio de Atoyac de Álvarez, 1654 m a.s.l., INIRENA 2802, CIG 1496 • 5 km S of La Laguna, on road from San Luis La Loma to Bajitos de la Laguna, Municipio de Técpan de Galeana, 1686 m a.s.l., INIRENA 2803 CIG 1502 • Bajitos de la Laguna, Municipio de Técpan de Galeana, INIRENA 2804, CIG 1632 • Jaguar Research Facility, Municipio de Técpan de Galeana, INIRENA 2805, CIG 1457 • 4.2 km S of La Laguna, on San Luis San Pedro – La Laguna Rd., Municipio de Técpan de Galeana, 1620 m a.s.l., INIRENA 2810, JRV 0362.

Tropidodipsas philippii.— Mexico: Colima • 2 km E of Hwy. 54 frontage road on road to Ixtlahuacán, Municipio de Ixtlahuacán, 346 m a.s.l., INIRENA 2782, CIG 1503 • San Gabriel, Municipio de Ixtlahuacán, 490 m a.s.l., CIG 0902 • 2 km S of Minatitlán, on Hwy. 98, Municipio de Minatitlán, 712 m a.s.l., JAC 28262 • 16–24 km SW Colima, LACM 59146 • Jalisco: 8.6 km N of El Tuito on Hwy. 200, Municipio de Cabo Corrientes, 702 m a.s.l., ENS 11639 • Nayarit: Las Mesas, Municipio de Tepic, 338 m a.s.l., JAC 24811 • Michoacán: 2.4 km N of Hwy. 200 on road to Ostula, Municipio de Aquila, 138 m a.s.l., JAC 27923 • Sinaloa: 10.1 km NE of Concordia turnoff on Hwy. 40-D cuota, on road to Durango, Municipio de Concordía, 287 m a.s.l., JAC 30601 • 85.3 km N of Mazatlán, LACM 7118 • 57.9 km N of Mazatlan, KU 73640; 50.9 km N Mazatlan, LACM 7119 • between Escuinapa and Palmilla, LACM 7117 • Teacapan, LACM 7116.

Tropidodipsas sp. cf. philippii.— Mexico: Oaxaca • 5.1 km S of Jalatengo, Municipio de Candelaria Loxicha, 1390 m a.s.l., KU 137655 • Santa Rosa, Distrito Lachao, Municipio de San Juan Lachao, UCM 49372 • 27.4 km S of Juchatengo, Municipio de San Juan Lachao, 1829 m a.s.l., LACM 104321.

Tropidodipsas tricolor sp. nov. — Mexico: Guerrero • 1.5 km east of Río Verde, Municipio de Atoyac de Álvarez, 971 m a.s.l., INIRENA 2800, CIG 1837 • 4.5 km NW of Mixtecapa, on road to Malinaltepec, Municipio de Malinaltepec, 1815 m a.s.l., INIRENA 2798, CIG 1863 • Oaxaca: 26 km N of Putla Villa de Guerrero, on Putla Villa de Guerrero - Oaxaca Hwy., Municipio of Putla de Guerrero, 1785 m a.s.l., INIRENA 2799, CIG 1596.