156 



THE EXTINCT BATRACIHA, REPTILIA 



B. Kinnc, Director of the Squankum Company's marl excavations, Squankum, Monmouth 

 County, N. J. 



TLEURODIRA. 



This division of the order, now found only in the southern hemisphere, had, in Meso- 

 zoic and Cainozoic time, as is known to geologists, a much more extended distribution. 

 It has presented to various naturalists the appearance of a repetition under another type 

 of structure, of the groups of Cryptodira. Agassiz, in his contributions to the Natural His- 

 tory of the United States, Vol. I., states that he believes it to form a series of families 

 parallel with those of the other suborder; but he does not attempt to define them. No 

 gives as types of these families Chelys, Sternothacrus, Pclomcdusa, Hydraspis, Chelodina, 

 and Podocnemis. After some examination of their structure, assisted by an essay on 

 their cranial characters by Dr. Gray* I believe that four such families exist, the types 

 of which are Pclomedusa, Sternothaerus, Hydraspis, and Podocnemis. I have al- 

 ready indicated the fact that Pelomedusa has the foot of the Testudinidae. I 

 also find that it has the rudimental intersternal bone, as figured by Waglcr in 

 1'odocnemis, and that Sternothacrus has this bone complete on each side, en- 

 tirely separating the hyo- and hypostcrnals, as in the extinct, and till now uncharacterized 

 family of the Plcurosternidae. The Hydraspididae have neither this bone nor a zygo- 

 matic arch, but a peculiar parieto-mastoid arch, as in the Chamaeleons. These characters 

 are shared by Chelys, Chelodina and others. Podocnemis adds to the zygomatic arch, 

 the latcral-intersternal bone, an Emydoid loot, and no parieto-mastoid arch. 



The extinct species of the Pleurodira, as yet found in Europe, belong to the Sterno- 

 thaeridae and Podocnemididae. Tins T have readily determined from the good descrip- 

 tions and figures given by Professor Owen in the Paleontographical Society's volumes. 



STERNOTHAERIDAE. 



To this family belongs the Platemys bullockii Owen, from the lower Eocene. It repre- 

 sents a genus which I call DlGERRHUM, which differs from Sternothaerus in having the an- 

 terior lobe of the sternum immobile, and two ranges of marginal plates, as in Pl'euroster- 

 num and Chelone. 



PODOCNEMIDIDAE. 



To this family belong Emys laevis and Platemys howerbanldi of Owen, who com- 

 pares the latter species to Podocnemis. So far as I can see they both appear to belong 

 to the genus Podocnemis, and may be called Podocnemis laevis, and P. bowcrbankn. 



To this family may perhaps also belong the genus. 



*Proc. Zool. Soc, London, 1804. 



