CHECKLIST OF THE SNAKES OF MEXICO 49 



Genus DIPSAS Laurenti" 



Dipsas Latjrenti, Specimen medicum exhibeus synopsin reptilium . . ., 1768, p. 89. 

 Sibynomorphus Fitzinger, Systema reptilium, 1843, p. 27 (type, Dipsas mikani 



Sclilegel). ♦ 



Leptognathus DuMfiRiL, M4m. Acad. Inst. France, vol. 23, 18.53, p. 467 (type, Dipsas 



pavonina Schlegel ; a homonym of Leptognathus Swaiuson, 1839 [fishes]). 

 Cochliophagiis Dumertl, ibid., pp. 467—468 (type, C. inaequifasciatus Dum^ril and 



Bibron, of "Amerique m^ridiouale"). 

 Mesopeltis Cope, Proc. Acad. Nat. Sci. Philadelphia, vol. 18, 1866, p. 318 (type, 



M. sanniolus Cope). 

 Astheiiogmithus Bocourt, Bull. Soc. Philom. Paris, ser. 7, vol. 8, 1884, p. 141 (type, 



Petaloffnathus multifasciatus Bocourt [ = D. dimidiatus]). 



Genotype. — Dipsas indica Laurenti. 



Range. — From Colima on the Pacific coast and from the Isthmus of 

 Tehiiantepec on the Atlantic southward to northern Argentina. 

 Species. — About 45 ; 7 occur in Mexico.-^ 



KEY TO MEXICAN SPECIES OF DIPSAS 



1. Scales in 13 rows medially gaigeae 



Scales in 15 rows medially 2 



2. Mental followed by a single, azygous scale 3 



Mental followed by one or more infralabials, in contact on midventral 



line 4 



*• There is much divergence of opinion regarding tlie generic distinctness of groups to 

 which the names Tropidodipsas, Sibon, Sibynomorphus, and Dipsas (as well as others, 

 extralimital and not bearing upon the names for Mexican groups) have been applied. The 

 number of species and variety of form involved are extraordinary and lead to the belief 

 that several genera can and should be recognizable. Yet Parker (Ann. Mag. Nat. Hist., 

 ser. 9, vol. 18, 1926, pp. 205-206) has shoven rather conclusively that the few si)ecie3 

 referred to Dipsas (cf. Amaral, Mem. Inst. Butantan, vol. 4, 1929, pp. 200-201) show a 

 closer relationship to various species of Sibynomorphus {ef. Amaral, op. cit., pp. 195-200) 

 than to each other and that the single character (presence or absence of pterygoid teeth) 

 supposed to distinguish the two genera is variable within several species. In 19.36 Amaral 

 (Mem. Inst. Butantan, vol. 10, p. 127) was not prepared to accept Parker's conclusions, 

 hut in the absence of any tangible means for distinguishing the two groups, as previously 

 defined, we are compelled to synonymize them. Prado (Mem. Inst. Butantan, vol. 14, 1940, 

 p. 13) is of like opinion. 



Although the genus Sibon (as of Amaral, op. cit., 1929, p. 194) is clearly a close ap- 

 proach of colubrines and dipsadines (as defined by Amaral, Proc. New England Zool. Club, 

 vol. 8, 1923, pp. 95-96), the broad articulation of the pterygoids with the quadrate is not 

 matched by any species of Dipsas (including Sibynomorphus) , all of which have short 

 pterygoids that extend straight posteriorly instead of diverging obliquely toward the 

 quadrate, at least so far as is known in the literature. Parker's (loc. cit.) mention of a 

 relatively very large number of pterygoid teeth (20) in Dipsas catesbyi does not, however, 

 correspond well with the concept of a short pterygoid in Dipsas. It may well be that 

 Sibon too belongs in Dipsas, but evidence available at present requires its retention as 

 a separate genus. 



Tropidodipsas is much more compact and homogeneous than Dipsas and is therefore more 

 certainly a natural group than the latter, widely variable, genus. It has no single distinc- 

 tive character but is clearly distinct from Dipsas on the basis of the normal pterygoids and 

 from Sibon through the absence of enlarged vertebral scales. 



Thus for the groups that enter Mexico we retain the names Sibon and Tropidodipsas as 

 distinct genera in their status quo, while we combine Dipsas and Sibynotnorphus. 



" See Species Inquirendae, p. 200. 



