104 G. R. Wieland — On Marine Turtles. 



portant comparisons. All taken together display the great 

 variations seen in particular in the last five Testudinate cervi- 

 cals. I may explain that I have introduced a modified nomen- 

 clature I proposed in this Journal for August, 1899, p. 168, 

 since the ordinary and incomplete terminology does not ade- 

 quately express the complicated forms seen in Testudinate 

 cervicals. 



The cervicals of Toxochelys are distinctly intermediate in 

 character between those of Chelydra and the Chelonidce^ being- 

 most like the former. The ends of the sixth, seventh and 

 eighth broaden, but there are no distinctl}^ biconcave, bicon- 

 vex, or flat terminations, these vertebra still being procoelous 

 (coelocyrtean). Their centra have strongly marked elongate 

 and thin or blade-like keels, quite similar to those of the sixth 

 and seventh, but not the eighth centrum, of Chelydra. The 

 total length falls far short of that seen in the ChelydridcB. 



In Archelon, the sixth, seventh and eighth cervicals were 

 found in place in the type specimen, as well as several others. 

 All are characteristically procoelous (= coelocyrtean), and none 

 have their anterior ends markedly broadened as in Toxochelys. 

 They are also relatively much shorter than in Toxochelys^ and 

 very robust (loc. cit.). I have estimated the cervicals of the 

 type specimen of Archelon as having a length of 'TS'". The 

 cranial length must be about the same. But in Toxochelys 

 the total length of the cervicals is about one and a half times,, 

 and in Chelydra twice that of the cranium. We cannot doubt 

 that the fourth cervical was biconvex (Cyrtean), since it is so 

 in all known marine Testudinates. The vertebrae of Archelon 

 are on the whole rather more primitive than in any other 

 marine turtle, and it is certainly very interesting that there 

 should be a closer agreement with Toxochelys than any other 

 form. 



IV. Bearing of the Foregoing Data, and Classification. 



A phylogenetic classification of the marine Testudinates will 

 still be held more or less difiicult to deduce, according to the 

 view that is taken of the much debated descent oiDermochelys. 

 In weighing the evidence at jDresent available, however, it 

 needs to be borne in mind that the wide distribution of the 

 turtles in latitude and time necessitates the consideration of 

 slighter differences than in the case of more variant forms. 

 While this must finally be a great advantage, it is a fact that 

 at present brings home to us with force our imperfect, but 

 happily rapidly increasing, knowledge of the • fossil record. 

 Again, there is a constant danger that in such a case one may 

 regard evolution as having taken a far simpler course than has 



