APPENDIX C. — REPTILES. 359 



in that respect from Phr. platyrhinos, modestum, and douglassii, 

 with which it has in common the small and uniform scales on the 

 inferior surface of the head. In the mean while, that same charac- 

 ter distinguishes it from Phr. cornutum and coronatum. The femoral 

 pores are very conspicuous. The plates which line the jaws are 

 proportionally much smaller than in any other species. 



The genus Phrynosoma is a truly American type. The distri- 

 bution of its species over the continent is as follows : — Phr. orhicu- 

 lare in the vicinity of the city of Mexico and in Sonora ; Phr. cor- 

 nutum, from Texas to Arkansas as far as the Rocky Mountains ; 

 Phr. platyrhinos, in the valley of the Great Salt Lake ; Phr. mo- 

 destum, in the valley of the Rio Grande del Norte ; and Phr. coro- 

 natum and Phr. douglassii, in Oregon and California ; the latter 

 species extending as far eastward as the valley of the Great Salt 

 Lake, where it has been observed in company with Phr. platyrhinos. 



The division of phrynosomas into two groups, according to the 

 position of the nostrils, whether situated within the internal margin 

 of the superciliary ridge or at its extremity, would bring into one 

 group Phr. orhiculare, coronatum^ and douglassii, and into another 

 Phr. cornutum, platyrhmos, and modestum. On the other hand, if we 

 subdivide the species according to the shape of the profile, we 

 would have on one side : Phr. orbicular e, cornutum, and coronatum, 

 and on the other Phr. douglassii, platy rhinos, and modestum. Phr. 

 douglassii is the only species in which the cephalic spines remain in 

 an undeveloped state. Phr. coronatum and cornutum have a double 

 series of horizontal pyramidal scales on the periphery of the 

 abdomen, while in Phr. orhiculare, douglassii, and platyrhinos, 

 there is only one series of these, very small already in the latter, 

 and totally absent in Phr. modestum. The difficulty of establishing 

 subdivisions in this genus is thus plainly evident, and shows how 

 natural and well circumscribed it is when considered as a whole by 

 itself. 



We give now the diagnostic characters by which the six species 

 of Phrynosoma may be distinguished. 



L Phrynosoma orbiculare, Wiegm. — Profile declive, tips of 

 of jaws protruded, nostrils situated at the anterior extremity of 

 the superciliary ridge. Occipital and temporal spines strong and 

 well developed. One row of pyramido-horizontal and abdomino 

 peripheral scales. Scales on the inferior surface of head, small, 

 of a general uniformity, although irregular in shape. The plates 

 on the margin of the jaws are inconspicuous, and very little larger 



