72 H. H. NEWMAN. 



specimen of Eretnwclielys imbricata, a fossil species in which are 

 found " small polygonal plates of the same shape as those of 

 Dermochelys, suturally connected with the third, fourth, fifth and 

 sixth costal plates." "A form between the Dermochelydae and 

 " Thecop/iora" (Dollo) is represented by the oldest known turtle, 

 Psephodenna alpinuin, H. v. Meyer, from the Triassic of the 

 Bavarian mountains, preserved in Munich. In this highly in- 

 teresting specimen, never mentioned in monographs on the 

 Testudinata, we have certainly not less than 193 plates suturally 

 united." According to Zittel's Paleontologie, Baur later ex- 

 pressed the opinion that Psephodenna may not be a chelonian 

 at all, but perhaps a nothosaurus. Thus doubt is cast upon 

 the best link in the chain of evidence. That all the principal 

 groups of Chelonia were in existence in the earlier Mesozoic ages 

 and that Palaeozoic Chelonia are entirely unknown are familiar 

 facts. So our attempts to reconstruct an ancestral condition 

 must be made largely on the basis of embryology and compara- 

 tive anatomy. 



2. Nor is cinbryological evidence of chelonian phylogeny at 

 all conclusive. The best and most recent study of the develop- 

 mental history of the chelonian carapace and plastron was made 

 by Goette in 1899. He summarizes the previous literature on 

 the subject and shows that the main question at issue is that of 

 the character of the neural and costal plates. Some authors, 

 principally paleontologists, have maintained that these structures 

 have a dermal origin and hence arise independently of the inter- 

 nal skeleton. Others hold that these plates are mere outgrowths 

 of the ribs and spinal processes of the vertebras. Goette favors 

 the latter view and presents as evidence of its correctness a series 

 of very careful embryological studies. 



Suspecting that there might be some flaw in Goette's work, I 

 repeated much of it, using the embryos of Chelydra serpcntina 

 and Grapteinys geograpJiica, and have satisfied myself that the 

 neural and costal plates actually do originate as outgrowths of a 

 differentiated tissue that surrounds the neural and rib cartilages. 

 Whether this differentiated tissue be true periosteum, as Goette 

 affirms, or simply a somewhat denser portion of the connective 

 tissue that fills the space between the epidermis and the cartilagi- 



