THE SNAKE GENUS TRIMORPHODON — SMITH 155 



12. A roughly Y-shaped mark on parietals, the arms forking just behind frontal, 

 the mark usually enclosed by dark color posteriorly ; belly with some, sub- 

 caudal surface with numerous dark marks ; blotches on body 23 to 32. 



upsilon 



No similar mark on head ; dark color of head sharply truncate near posterior 

 edge of parietals, with a narrow or broad, light indentation along parietal 

 suture t*^ 



This study was completed, and a number of specimens on which it 

 is based was collected, during my tenure of a Walter Rathbone Bacon 

 Traveling Scholarship of the Smithsonian Institution. I am much 

 indebted to Dr. E. H. Taylor and L. M. Klauber for the loan of 

 numerous important specimens and for invaluable advice and criti- 

 cism, without which the study would have been impossible. 



Genus TRIMORPHODON Cope 



TRIMORPHODON PAUCIMACULATUS Taylor 



Trimorphodon paudmaculatus Tatxor, Kansas Univ. Sci. Bull., vol. 24, pp. 

 527-529, pi. 46, fig. 1, 1936 (1937) (Mazatlan, Sinaloa) ; ihid., vol. 25, p. 360, 

 pi. 35, fig. 3, 1938 (1939).— Klauber, Trans. San Diego Soc. Nat. Hist., vol. 

 9, p. 185, 1940. 



Diagnosis. — Large V-shaped marks on head, these not continued on 

 neck but disappearing laterally just behind head; hemipenis long, 

 with a middle belt of enlarged spines; ventrals 251 to 253, caudals 

 76 to 84; anal entire; blotches on body 20 to 25, a little more than 

 twice as long as spaces between; secondary bands reduced to small 

 lateral spots, not extending dorsally; tail blotches 10 to 13. 



Specimens examined. — Two, including type. 



Locality/ records. — Mazatlan and Presidio, Sinaloa; San Bias, 

 Nayarit (U. S. N. M. No. 46617). 



Bemarks. — The San Bias specimen is in very poor condition but 

 can be seen to have very broad blotches ; it has 84 caudals. 



This species, I believe, possesses the pattern of the ancestral type 

 of lambda, lyrophanes, and vandenburghi, which I interpret as being 

 direct derivatives of it. It is, moreover, near the ancestral type of 

 the whole group, since it is a little less specialized, in pattern, than 

 the direct ancestor {quadruplex) of the other member of the group 

 {hiscutatus) . 



TRIMORPHODON LAMBDA Cope 



Trimorphodon lamhda Cope. Proc. Amer. Pliilos. Soc, vol. 23, pp. 286-287, 1886 

 (Guaymas, Sonora). — Taylor, Kansas Univ. Sci. Bull., vol. 25, pp. 360-361, 

 pi. 35, fig. 4, 1938 (1939). 



Trimorphodon lyrophanes Klauber., Trans. San Diego Soc. Nat. Hist., vol. 9, 

 pp. 181-187 (part), 1940. 



Diagnosis. — Large V-shaped marks on head, these not continued on 

 neck but disappearing laterally just beliind head; hemipenis long, 



