G. R. Wieland—On Marine Turtles. 105 



really been the fact. It would appear tliat several hypotheses 

 yet require coDsicleration, as follows : 



(1) All the known marine Testuclinates may be the de- 

 scendants of a sin2:le littoral species. 



(2) Derinochelys on the one hand, and all the other marine 

 forms on the other hand, may have descended from two dif- 

 ferent littoral species of the same genus, or from different 

 genera. 



(3) Dermoclielys^ Toxochelys^ Protostega^ and the living 

 Chelonidw may represent the descendants of four genera of 

 the same, or closely allied families. 



(4) Dermochelys is of ancient descent, and stands phyleti- 

 cally and morphologically opposed to all other Testndinates. 



Donbtless the final trnth will be fonnd to lie somewhere be- 

 tween the first and last extremes. Certainly it is difiicult to 

 overthrow the conclnsion as to the general fact of descent as 

 thus expressed and as defended with snch signal ability by 

 Banr :* 



" Dariiber aber ist kein Zweifel dass Dermochelys nnd 

 Psephophorous keine nrsplinglichen Formen sind, sondern 

 dass sie von wahren ' Thecophoren ' nnd zwar von den 

 'Pinnaten' abstammen, nm mich hier dieses Ansdrncks zn 

 bedienen." 



Dollo,t originally a strenuous opponent of this view, has 

 recently adopted it. Taking up the question in further detail, 

 he holds Dermochelys to be descended from a pelagic Theco- 

 phore with an extremely reduced carapace and plastron, but 

 the descendant of a littoral Thecophore with a fully developed 

 carapace, and a plastron without fontanelles. And this eminent 

 scientist has proposed the ingenious hypothesis that such a 

 Thecophore again acquired littoral habits, resulting in the 

 formation of a heavy mosaic carapace, which, with a second 

 resumption of pelagic habits, again began to disappear, and is 

 still in process of reduction. The persistence of the nuchal 

 is held to be due to its value as an attachment for the nuchal 

 ligaments. However involved such an evolutionary process 

 may appear, it is skilfully presented, and has much in its 

 favor. 



On the other hand, Hay| has presented at considerable 

 length facts favoring a very early origin of the Dermochelan 

 line. 



* G. Baur.— Biologisches Centralblatt, Band ix, 1889, p. 191 (Erlangen). 



f L. Dollo. — Sur rorigine de la Tortue Lutli (Dermochelys coriacece). Ex- 

 trait, Bull. Soc. roy. des Sciences Med. et Nat. de Bruxelles, Seance 4 fevrier, 

 1901. 



X O. p. Hay. — On Protostega, the Systematic Position of Dermochelys, and 

 the Morphogeny of the Chelonian Carapace and Plastron. American Nat- 

 uralist (Boston), Dec. 1898. 



