1 1 00 CLASS REPTILIA. 



plastron which not improbably belong to the same form. Bothremys 

 differs from Podocnemis by the presence of a distinct vomer. It is 

 not improbable that allied forms occur in the Cretaceous of New 

 Zealand. The only existing genus which appears to be represented in 

 a fossil state is the above-mentioned Podocnemis, of South America 

 and Madagascar, which occurs in the London Clay and the Eocene 

 of Northern India. This genus includes the largest existing repre- 

 sentative of the section. The carapace has seven neural bones, 

 and the mesoplastrals are small, and do not meet in the middle 

 line. The shell of a large Chelonian from the London Clay, which 

 has been referred to this genus under the name of P. Delabechei, 

 may not improbably belong to the genus Dacochelys. The latter is 

 founded on a mandibular symphysis from the same deposits which 

 is characterised by a large spine-like process on its oral surface, 

 and the serrated margins of the alveolar borders. Its serial position 

 depends on whether it is specifically identical with the above- 

 mentioned shell. 



Family CHELYiDiE. 1 — In this family the shell is much thinner 

 than in Plesiochelys, and is characterised by the absence of the 

 mesoplastrals, and the reduced number of neural and suprapygal 

 bones ; while both the pubis and ischium unite with the plastron. 

 The skull has an incomplete inferior temporal arcade, owing to the 

 absence of the quadratojugal ; and is further distinguished by the 

 separation of the prefrontals by the frontals ; the distinct nasals 

 (except in Ckelys); by the vomer dividing the palatines; and by 

 the persistence of the suture in the mandibular symphysis. The 

 temporal fossae are open, but there is an arch connecting the parietal 

 with the squamosal, not found in the Pelomedusidcz, and which is 

 probably a remnant of the earlier type of roof. The fifth and eighth 

 cervical vertebrse are biconvex. The neck cannot be fully retracted 

 within the carapace. As typical genera we may notice the South 

 American Chelys, Hydrastis, and Plaiemys ; and the Australian 

 Chelodina, Emydura, and Elseya, in which neural bones are absent. 

 Remains of Chelodina and Emydura occur in the Pleistocene of 

 Australia ; while Hydraspis is found in a fossil state in the Lower 

 Eocene of India, and Platemys has been recorded from the Creta- 

 ceous of North America. 



Family Miolaniid^. — This is an extinct family represented only 

 by the remarkable Mtolania, from the Pleistocene of Australia, of 

 which the remains were originally referred to the large Va?-anus of 

 the same deposits. This family, according to Mr Boulenger, occupies 

 a position in the present section somewhat analogous to that filled 

 by the Chelydridce among the Cryptodira ; the caudal vertebrse 



1 Frequently incorrectly given as Chelydidce. 



