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Show \ APPENDIX C.- REPTILES. 859 in. that respect from Phr. platyrhrnos, modestum, and doUglwsii, with which it has in common the small and uniform scales on the inferior surface of the head* Jn the mean while> that'same character distinguishes it from Phr. wmutum 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 distribution, of its opecies over the continent is as follows ;- Phr. orbicu-lare in the vicinity of the city of Mexico and in Sonora; Phr. cor- . nutum. y froni Texas to Arkansas'as far as the Rocky Mountains; Phr. platyrhinos, in the valley of the Great Salt Lake; - Phr. modestum, in the valley of the Eio Grande del Norte; and- PAr. coro? natum and Phr. douglassii9 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. platyrhino** • 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. orbiculare, coronatum, and douglasstit and into another Pht. cornutum, platyrhinos, and modestum. On the other hand, if we subdivide the species according t? the shape of the profile,- we would have on one side: Phr. orbiculare, corntitum, and coronatum, and on the other Phr. douglassii, platyrhinos, and mode$ tum. 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. orbiculare, 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 thitf 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. I. PHRYNOSOMA OBBICPLARB, Wiegm.- Profile deelive, tips of of jaws protruded, nostrils situated at the anterior extremity of the superciliary ridge. Occipital and temporal spine* strong, and well developed. One row of pyramido- horizontal and abdomino peripheral scales. Scales on the inferior surfaea 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 |