PHRYNOSOMA. 393 



is taken into consideration, we will have, on the one hand, those in 

 which these apertures are situated within the extension of the supra- 

 ciliary ridge : P. cornutum, regale, mccaUi, plaiyrhinum, and modes- 

 turn; and, on the other hand, P. orbiculare, hernandesl, douglassi, orna- 

 tissimujn, hrevirosirum, and corojiahim, in which these same apertures 

 are situated upon the extension of the supraciliary ridge : hence, more 

 lateral than in the former group. At one time, the pyramidal scales 

 at the periphery of the abdomen were thought of some value in that 

 respect, being either disposed upon one or a double series : there is 

 a double row of them in P. cornutum and coronatum, and one series 

 only in P. orhlcidare, douglassi, Jiernandesi, ornatlssimuin, hrevirosirum, 

 regale, and platyrhirmm ; P. mccalli exhibits a triple series of them, 

 and in P. modestum, they are entirely absent. The profile of the 

 head, whether the snout is protruding or abbreviated, would bring 

 into one group P. orhiculare, Jiernandesi, ornatissimum, coronatum, cor- 

 nutum, and regale, and into another, P. brevirostrum, mccalli, platy- 

 rhinum, and modestum. P. douglassi, as it now stands, would enter both 

 groups; still, as it is probable, that there are yet two species combined 

 under that name, one may exhibit an abbreviated snout, and a protrud- 

 ing one in the other. If the abdominal scales are taken into consi- 

 deration, we will have on one hand P. cormdum, regale, mc'calli, and 

 modestum, although, in the two latter, they are but slightly keeled, 

 and, on the other hand, P. orbiculare, Jiernandesi, douglassi, ornatissi- 

 mum, brevirostrum, coronatum, and platyrJdnum, where they are smooth. 

 In neither case would we have a natural subdivision. The various 

 folds of the neck and shoulder, as well as the auricular apertures, are 

 of no better avail in this respect. Indeed, minor subdivisions of the 

 genus PJirynosoma have hitherto appeared to us as a breach into the 

 natural affinities of its species, and, at the time we offered " A Mono- 

 graphic Essay" of the latter, we held it as an idle attempt.* 



After a laborious study of one of the most extensive collections of 

 these Saurians, now in the Museum of the Smithsonian Institution, 

 we offer the following Prodrom, as embodying our present thoughts 

 upon the subject. 



* In Stansbury's Exploration of the Valley of the Great Salt Lake of Utah, 1852, 



354. 



99 



