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Show 354 APPENDIX C.- REPTILES, A MONOGRAPHIC ESSAY ON THE GENUS PHBYNOSOMA. BY CHARLES GIBAKD. 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 Philadelphia, have enabled us carefully to study and compare the different 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 conspicuous 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 t 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 prominent 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 |