328 AMERICAN TESTUDINATA. Part II. 



upon its junction with the carapace. On the free skin, the epidermis is also formed 

 into a kind of scales ; but upon the wings and paddles the scales become stiff and 

 hard, and they are larger along their inner and outer edges, as they are also where 

 the skin fits close to the bones of the head. The scales on the inner edge of 

 the paddles recall the large feathers of the wings of birds by their arrangement 

 and their elongated form. The central scale upon the skull is the largest. The 

 horny sheath of the bill is very strong. 



As in Sphargididte, the jugal, parietal, postfrontal, temporal, and mastoid bones 

 of the ChelonioidiB unite to make a bony covering over the whole head back of the 

 eyes, protecting the temporal muscles and the brain-box, and projecting even back 

 over the first neck vertebrae ; but here the parietal bones are not so exclusively 

 devoted to this office as in the Sphargididae, for they reach down to the floor of 

 the skull, and add to the length of the brain-box in front. The temporal bones do 

 not, as in the Sphargididas, add to the width of the head, but reach directly forward 

 and so bring the bony arch further down over the attachment of the temporal mus- 

 cles to the lower jaw. The prefrontals meet before the frontals, and so carry the 

 top of the skull further over the nasal region. The alveolar margin of the upper 

 jaw has not the deep depressions or the sharp, tooth-like projections observed in 

 Shargididfe. The horizontal alveolar surface is very broad all round the upper 

 jaw, and the palatines project inward from the suture Avith the maxillaries, unit- 

 ing, together with the end of the vomer and the alveolar surface, to make a 

 very broad roof below the palate proper. The jiassages from the nasal cavity 

 necessarily descend very obliquely over this roof, to oj^en into the mouth behind 

 it. The lower jaw is very thick, especially at the symphysis, and its alveolar sur- 

 face is broad. The neck moves somewhat up and down upon the first dorsal ver- 

 tebra, and the head may be drawn back so as to reach the carapace, but it can- 

 not be withdrawn under it. 



The size of the members of this family is very great, much greater than the 

 average size of the Amydte, though they do not grow so large as the Sphar- 

 gididae. The food of most of them is known to consist of aquatic plants, sea- 

 weeds, and the like. Like all the herbivorous animals, the Chelonioidse are shy 

 and inoffensive ; they do not bite, even when hard pressed, but strike with their 

 powerful flappers, and try to make their escape by increased speed. The North 

 American Chelonioidaj lay their eggs towards the end of May or in the beginning 

 of June. They lay a large number of them, about one hundred at a time, and 

 even more, which they deposit on shore, in the dry sand. These eggs are not 

 very large in comparison to the size of the animal, and not perfectly spherical, 

 their orbicular outline being more or less irregular. I have no reason to trust 

 the reports that they lay eggs more than once in a year. 



