THE SNAKE GENUS TRIMORPHODON SMITH 165 



not now be stated. It is remarkable that the reversal of pattern 

 begins anteriorly precisely at the frontal-prefrontal suture; anterior 

 to this suture the head pattern is normal, with a light snout and a 

 light, longitudinal median line with darker sides; posterior to this 

 suture the light color is very sharply changed to dark, and vice versa, 

 with the exception of the black borders, which outline the markings 

 and which remain constant. 



Wliile the head pattern of forhesi is very different from that of 

 other species of the group, it cannot be considered in differentiation 

 of the species from uqysilon^ since there is a strong possibility it may 

 be anomalous. There are numerous other unique characters in 

 forhesi. No specimens of other species of Trimorphodon of the 

 upsilon group have the anterior loreal divided; and no other of that 

 group has the fifth and sixth labials entering the eye. These charac- 

 ters, combined with a faintly marked belly and white, unmarked 

 subcaudal surface {upsilon has the belly, and especially the tail, 

 distinctly dark-mottled) ; number of rhombs (fewer than in upsilon 

 and tau with a minimum of 23, and more than in collaris with 16) ; 

 narrow black borders of the rhombs (broad in tau., possibly in 

 collaris) ; length of rhombs on middorsal line (as long as in collans., 

 longer than in tau or upsilon) ; all define a species very different from 

 any other of the upsilon group. 



The closest relative of forhesi., I believe, is upsilon^ the general 

 appearance of the dorsal rhombs is much the same. The elimination 

 of the ventral markings and lightening of the dorsal markings may 

 be compared with the same tendency in other deserticolous reptiles 

 which develop a faded pattern. The remarkable changes in cephalic 

 scutellation bring to mind a somewhat similar, recent change in van- 

 denburghi of the other {biscutatu^) group, in which a single anal is 

 developed. Neither of these two species is otherwise greatly (although 

 somewhat) different from its closest relative. 



The type is from a semiarid region. So far as known upsilon is 

 restricted to more humid areas. 



TRIMORPHODON COLLARIS Cope 



Trimorphodon collaris Cope, Journ. Acad. Nat. Sci. Philadelphia, ser. 2, vol. 8, 

 p. 131, 1875 ("Orizaba").— SuMiCHBA ST, La Naturaleza, vol. 6, p. 14, 1882. 



Trimorphodon latifascia Tatlor (part), Kansas Univ. Sci. Bull., vol. 25, pp. 

 364-365, 1938 (1939). 



Diagnosis. — A light, tranverse nuchal collar; an interocular light 

 bar; snout light; 16 bands on body, the longest covering 13 scale 

 lengths middorsally, eight on venter ; spaces between blotches covering 

 four and one-half to six scale lengths middorsally. 



/Specimens examined. — The only one known, the type (U. S. N. M. 

 No. 26499). 



