CuAP. III. GENERA AND SPECIES OF CIIELONIOID.E. 375 



SECTION III. 



THE GENKUA AND SPECIES OF CUELONIOIDJE. 



Three well marked genera, belonging to this flimily, occur along the coasts of 

 the United States; namely, Chelonia, Eretmochelys, and Thalassochelys. The most 

 important generic characters thus far observed relate to the structure of the 

 mouth, and indicate much difference between them, in the manner of eating, and, 

 perhaps, also in the kinds of plants upon which they feed. In Cheloxia the 

 jaws act like straight-edged shears, cutting from behind forward ; the mouth is 

 bluntly curved about the front end ; the outer alveolar edge of the lower jaw 

 falls from the angle forward till just at the end, where it rises to a small, sharp 

 projection; the l)ill along this edge is deeply serrated; its teeth act against sharp 

 ridges, which cross, from above downward, the inner vertical surface of the bill 

 of the upper jaw. In Eretmochelys the jaws are drawn out forward, as it were, 

 and the mouth is narrow and long; at the front end the cutting edges of the two 

 jaws project toward one another beyond their general level, so that as the jaws 

 close, these edges approach each other first at their front and hind ends; the 

 cutting edge of the lower jaw is short, as the upper surface is I'oimded for some 

 distance in front of the angle ; the cutting edges are sharp, but not serrated. 

 In Thalassochelys the jaws are prolonged toward one another at the front ends 

 into strong, pointed beaks, but not drawn out forward as in Eretmochelys; as 

 the jaws close, they approach one another first at the front and hind ends; the 

 alveolar edge of the lower jaw is deeply concave, and rises higher at the point 

 than at the angles ; the alveolar edge of the upper jaw rises on each side of 

 the beak, and curves downward under the eye ; the alveolar edges are blunt, and 

 not serrated. 



I am not aljle to express an opinion upon the value of the genera Ilalichelys 

 and Lejjidochelys, as I have not enjoyed an opportunity of examining myself 

 the species upon which they are founded.^ But I can state that there occur, 

 among the fossils of the reefs of Florida, remains of a large marine Turtle 

 which diflers generically from the other species found alive al)Out tlie reefs. I 

 am indebted for a splendid skull of this Turtle to one of my pupils. Mr. The- 

 odore Lyman, of Boston; and I have obtained myself other fragments of the 



^ These {renera were proposed by Fitzinger in his Merr., Chelonia atra, Auct., and Lepidochelj'S for the 

 Systeniii Ufpliliiini ; Ilalicliclvs for the C'arcUa atra, Chelonia olivaeea, Escli., of tlie Paeitic. 



