130 CHELONIA. 



In the one species of which the entire carapace is known (fig. 30) 

 there is one entire neural and part of another between the first pair 

 of costals, so that there are three entire neurals and half of a fourth 

 in advance of the sulcus between the 2nd and 3rd vertebral shields. 

 There are also five costal shields. 



The costals from the Lower Greensand, described by Pictet and 

 Campiehe * as T. sanctce-crucis, present all the characters of those 

 of this genus, but are referred by Riitimeyer 2 to Plesiochelys as 

 P. rugosa. 



This genus has been considered to be allied to Trionyoc or Treto- 

 sternum ; but in the contour of the long vertebral shields, in the 

 elongated neural bones, and the nature of the sculpture it appears 

 to be related to Dermatemys, and it certainly has nothing to do 

 with Trionyoc. The carapace agrees with that of Dermatemys in 

 the late period at which the marginals unite with the costals, and 

 in the manner in which the extremities of the ribs underlie the 

 marginals. In Dermatemys there are, however, but four costal 

 shields, the neural bones are reduced to seven, and the second is 

 undivided, so that there are only two entire neurals and one half of 

 a third in advance of the sulcus between the second and third 

 vertebral shields. Another point of resemblance to Dermatemys is 

 found in the slight depth of the sulci marking the boundaries of the 

 epidermal shields, the same feature being observable in the Eocene 

 American genus Agomphus. 



Trachyaspis lardyi, Meyer 3 . 



The type species ; imperfectly known. Carapace without longi- 

 tudinal costal ridges ; vertebral shields wide, and extending a con- 

 siderable distance on to the costals. 



T. miocama, Delfortrie 4 , from the Middle Miocene of Bordeaux, 

 appears to be a closely allied form. 



Hob. Europe (Switzerland). 



48041. Cast of the proximal extremity of a costal bone. The ori- 

 ginal is one of the types, and was obtained from the Middle 

 Miocene of Mont La Moliere, near Neufchatel, Switzer- 

 land. It is preserved in the Museum at Lausanne, and is 

 described and figured by Meyer in the ' Palrcontographica/ 



1 Paleontologie Suisse, ser. ii. Foss. Cretac. de Ste.-Croix. pt. i. p. 36, pi. iv. 

 (18f)8-G0). 



2 N. Denkschr. scliw. Ges. Nut. vol. xxv. art. 2, p. 147 (1873). 



8 Loc. cit. 4 Act. Soc. Linn. Bordeaux, vol. xxvii. p. 420 (1869). 



