P H R Y N S M A. 391 



smooth or keeled, according to the species. On the breast and ante- 

 rior portion of the shoulders, several rows of the largest scales are 

 seen, very prominent, very acute posteriorly, and strong!}^ carinated 

 or keeled. The anterior and upper aspects of the thighs are likewise 

 provided with large scales, though much less conspicuously keeled 

 than at the shoulders. 



The tail is always depressed at its base : it diminishes very rapidly 

 posterior to the vent, becoming cylindrical toward its tip. The pyra- 

 midal and raised scales are sometimes more conspicuous upon its sides 

 and upper surface, than on the surface of the body itself. The scales 

 beneath, in the vicinity of the vent, have the general appearance of 

 those of the belly ; in the postanal groove, some larger scales may 

 occasionally be seen : here, the scales assume a subverticillated arrange- 

 ment; upon the conical portion of this organ, they are carinated, while 

 they are generally smooth about the vent. 



The fore and hind limbs are nearly equal-sized ; the latter, however, 

 being somewhat stouter. The fingers and toes, five in number, are 

 moderate : the first and fifth are the shortest, and either of equal 

 length or the fifth may be a little longer; the second and fourth some- 

 what longer than the first and fifth, and likewise either of equal length 

 or the fourth somewhat longer than the second ; the third is always 

 the longest. The scales extend all over the toes, overlapping even 

 the base of the nails : they assume a subtriangular shape, very much 

 acuminated posteriorly, and very distinctly keeled. The nails them- 

 selves are curved, compressed at the base, and very acute at the tip. 

 On the inferior surface of the hind limbs, along the thigh, a series of 

 pores is observed, the femoral pores, varying in number and conspicu- 

 ousness according to the species. The anal pores are totally absent 

 in this group. 



There is a structural peculiarity in some species worthy of a special 

 remark: we allude to the auricular apertures, which, in some instances, 

 are entirely hidden under the skin. When this fiict was first noticed, 

 upon a specimen from the Colorado Desert, it was made the ground 

 for the estabUshment of a new genus, under the name of Auota. The 

 same structure we find now, more or less transitory in Phrynosoma 

 modestum, described on a former occasion, though, at the time we 

 published its description, it was not apparent upon the specimens we 

 had examined. Subsequent collections, containing numerous indivi- 

 duals, threw all desirable light on this subject, by exhibiting every 



