THE SNAKE GENUS TRIMORPHODON — SMITH 163 



men evidently preserved just before shedding, so the color is greatly 

 obscured (No. 12419, Guadalajara) ; another specimen, nearly perfect, 

 from the same locality, has the whole ventral surface very heavily 

 pigmented. In this respect upsilon differs from typical specimens 

 of tau, collaris^ forbesi, and vilkinsonii and agrees with fasciolata 

 and latifascia. 



The hemipenis of a specimen from "Mexico" (with 30 body 

 blotches) is 26 caudals long; three large flounces, covering the length 

 of eight caudals; area of spines covering the length of four caudals. 



In general there appears to be an increase in number of body 

 blotches toward the east. Western specimens (three from Guada- 

 lajara, and Magdalena, Jalisco) have the fewest (23, 24, 25), while 

 specimens from eastern localities (Guanajuato, Hidalgo, Zacatecas) 

 have 27 to 32. 



TRIMORPHODON FORBESI, new species 



Eolotype. — U.S.N.M. No. 110402, male, from San Diego (about 

 5 miles south of Tehuacan), Puebla, collected by Dyfrig McH. 

 Forbes. 



Diagnosis. — A transverse nuchal collar, heavily suffused dorsally 

 with dark pigment, so tliat the first dorsal band is more or less con- 

 fluent with the dark head color; belly very light, dark markings 

 dim; no markings on ventral surface of tail; bands on body 21, the 

 first five covering 13, 8, 9, 10, 10 scale lengths, respectively; nine 

 supralabials, fifth and sixth entering orbit; anterior loreal divided; 

 a large light area on head, including posterior portions of supraocular 

 and frontal, and more than half (anterior) the parietals, indented 

 posteriorly by a dark area, which reaches nearly to the posterior tip 

 of frontal. 



Description of hoJotype. — Frontal as high as wide, portion visible 

 from above a little longer than its distance from prefrontals, as 

 long as internasals; latter two-fifths as large as prefrontals; length 

 of frontal equal to its distance from tip of snout; nasal completely 

 divided, anterior section somewhat smaller than posterior; anterior 

 loreal wedged between internasals and prefrontals, divided into an 

 upper and lower part; a large posterior loreal; on one side a small 

 subloreal, making a total of three loreals on one side, four on other; 

 three preoculars; three postoculars, middle smallest, lowest largest; 

 temporals 3-4-5 ; supralabials nine, fifth and sixth entering e3^e, fourth 

 smallest, sixth perhaps largest; infralabials 12, five in contact with 

 anterior chin shields, two with posterior; first infralabial largest; 

 anterior chin shields twice size of posterior. 



Dorsal scales smooth, with two apical pits, in 2&-23-16 rows; 

 supra-anal scales convex; ventrals 213; anal divided; caudals 77. 

 Total length 818 mm. ; tail 150 mm. 



