ORDER CHELONIA. IO9I 



known, but it was doubtless devoid of tessaras. The allied Psepho- 

 phorus, ranging in Europe from the Middle Eocene to the Upper 

 Miocene, and also found in the Upper Eocene of the United States, 

 is characterised by the presence of a complete tesselated carapace 

 and plastron. In the carapace the longitudinal rows of larger scutes 

 are not carinated, and are more approximated than in the existing 

 genus ; the carapace is also thicker than in the latter ; and there 

 are larger marginals. It is also suggested that the carapace may 

 have had horny epidermal shields. The skull is short and much 

 depressed. The existing genus Dermochelys (Sphargis) is represented 

 only by the well-known Leathery-turtle, and is characterised by the 

 absence of a tesselated plastron ; by the carination of the scutes of 

 the larger rows of the carapace ; by the comparative thinness of the 

 carapace, which is devoid of epidermal shields ; and by the longer 

 and more vaulted skull. It is, moreover, worthy of note that in 

 this, as in the preceding genus, there is a distinct nuchal bone at 

 the anterior extremity of the carapace, corresponding to the nuchal 

 of the Testudinata ; but there are no marginal ossifications. The 

 one existing species of Dermochelys attains a length of nearly five 

 feet, but a species of Psephophorus is estimated to have been as 

 much as ten feet in length. The skull of Eosphargis, although 

 much larger than that of Psephophorus, does not apparently indicate 

 a much larger carapace. 



Suborder 2. Testudinata. — This suborder, for which the name 

 Thecophora 1 is also employed, includes by far the great majority 

 of the order, or all those forms commonly known as Tortoises, 

 Terrapins, and Turtles. The group is characterised by the middle 

 region of the carapace being formed of bony plates, developed 

 primarily from the ribs and the neural spines of the dorsal vertebrse, 

 to which it is firmly welded. The outer surface of the carapace is 

 very generally smooth and overlain by horny epidermal shields, but 

 it may be sculptured and devoid of such shields. The parietal 

 bones of the skull in all cases send down vertical descending plates, 

 which may either unite directly with the pterygoids, or be separated 

 therefrom by the intervention of the columella or epipterygoid. It 

 may be observed that in nearly all the Mesozoic forms the vertebral 

 shields are very wide, and that this condition obtains in the young 

 of the later forms. This suborder may be divided into four sec- 

 tions ; one, and not improbably two, families of the third section 

 being of marine habits. 



Section i. Amphichelydia. — This section is formed for the 

 reception of certain extinct Chelonians, mostly of Mesozoic age, 

 which combine in a remarkable manner the characters of the two fol- 



1 This name is objectionable, as being employed for an order of Hydroid 

 Zoophytes {vide supra, vol. i. p. 203). 



