354 APPENDIX C. — REPTILES. 



A MONOGRAPHIC ESSAY ON THE GENUS PHRYNOSOMA. 



By CHARLES GIRARD. 



The numerous specimens of nearly all the known species of 

 this genus which are now preserved in the Smithsonian Institution, 

 together with those at the Academy of Natural Sciences of Phila- 

 delphia, have enabled us carefully to study and compare the 

 diiferent members of that most remarkable group, the result of 

 which we propose here to present. 



Indeed, there are no genera in the saurian order that can so 

 readily be distinguished as that of Phrynosoma. The body more 

 or less circular in shape, always depressed, sometimes flattened, 

 scattered all over with irregular and spine-like scales ; the solid 

 and subtriangular head provided with acute spines or tuberculous 

 knobs, the short and conical tail covered with scales similar to 

 those of the body, sometimes even more prominent, are as many con- 

 spicuous features, which must strike any one at the very first glance. 

 Their general aspect, perhaps their sluggishness, may recall to 

 mind a frog or a toad: hence the vulgar name of horned toads or 

 frogs. But the naturalist, with no hesitation, recognises in them 

 true saurians, inasmuch as the body, instead of being smooth, like 

 that of either toads and frogs, is covered, as just stated, with 

 scales of a peculiar character. Besides the spines of the head, the 

 tail, although short, is another feature by which they disagree 

 from both toads and frogs. So much when these animals are at 

 rest : as soon as they move, the observer cannot fail to be struck 

 with the fact that phrynosomas never jump or leap, as is the 

 case with the batrachians, to which they have been compared. 



If we look now more closely at the zoological peculiarities proper 

 to the genus Phrynosoma we will see that the vertex is a promi- 

 nent feature of the head, subtriangular or cordiform, with a sharp 

 and projecting margin, forming a carina which overlaps the orbits ; 

 sometimes it is terminated posteriorly by two spines, one on each 

 side. The occipital region generally presents the largest spines 

 in those species in which these exist as a prominent feature. The 



