Chap. III. GENERA AND SPECIES OF CIIELONIOIDiE. 383 



ginal row form more prominent points in Eretmochelys imbrieata than in Eret- 

 mochelys squarnata. Less marked tlifierences are further observed in the fonn oi' 

 the different scales, all of which coincide to show that the Eretmochelys of the 

 Atlantic and of the Pacific Oceans are distinct species. 



III. Thalassochelys, Fits. • 



The genus Thalassochelys was established by Fitzinger, in his systematic 

 arrangement of the Testudinata.^ The head is low, broad, and flat on top ; its 

 upper surface descends but little forward, and the nose is placed high, which is 

 made necessary by the height to which the roof of the mouth is raised under 

 it. The mouth is broad; the jaws are prolonged at the front end toward one 

 another to strong, pointed beaks, but they are not drawn out forward, as in 

 Eretmochelys. The outer edge of the upper jaw rises on either side of the 

 pointed beak, and then curves down under the eye. The vei-tical inner surface of 

 this jaw is very broad at the hind end ; it narrows forward to about midwaj', and 

 then again widens to the front end, where it is broadest. The horny surface of 

 the roof of the mouth is high at the hind end ; it curves down thence to about 

 midway, and then rises again to the front end, where it is highest. This curve 

 from end to end is uninterrupted at the outer edge; but from this edge the 

 surface descends inward and backward for some distance, then suddenly rises, like 

 a step in a staircase, and then again curves up gradually inward and backward 

 to its hind edge. The part in front of the step can hardly be called a 

 furrow, or its inner edge a ridge, for it descends gentlj^, and comprises about 

 half of the whole horny roof; there is a depression in its inner edge at the 

 s_)Tnphysis ; on either side of this depression, it has more tlian half the width 

 of the whole horny surface. It narrows backward, and before reaching its hind 

 end unites imperceptibly with the part in front of the step. It has a pit at 

 the front end of the symphy.sis. The lower jaw is high at the angle, and at 

 the front end is dra\vn out to a long, strong point, which is still higher than 

 the angle. The outer alveolar edge, from the angle to tlie point, is deeply 

 concave. The alveolar surfiice descends steeply inward, is very I)r(>;i(l at \hr sym- 

 physis, and narrows l)ackward to the angle. At its inner edge it rises to a 

 small ridge, and from the crest of the ridge it descends steeply and on one 



^ Entwurf einer Sysf. Anordn. der Srliildkrolen. E. Gray in the Cat. Brit. JIu-!. 1844, under the new 

 Ann. des Wiener Museums, 183G, 4to. It is main- name of C.nouana. Dumeril and Bibron consider 

 tained in tiie Syst. Amph. of 1843, and adopted by J. this genus simply as a sub-genus of Chelonia. 



