FAUNA. OF THE GOSAU FORMATION. 



693 



Another tooth has the same general character ; but the crown 

 appears more curved, with sharper lateral ridges and finer and more 

 numerous striations. 



In the possession of lateral ridges, as well as in the striated sur- 

 face of the crown, the teeth of this species approximate to those re- 

 ferred by Leidy to Hyposaurus ; but there is no correspondence in 

 vertebral characters. The vertebrae referred by the same author to 

 Thoracosaurus correspond in being procoelous, but differ in the posi- 

 tion and character of the tubercles for the articulation of the ribs, as 

 well as in the form and direction of the neural spine in the cervical 

 region. It is difficult to determine accurately the relation of the 

 species to Holops ; but the absence of the hypapophysis from the early 

 dorsal vertebra? will exclude comparison with that form, equally with 

 the contour of the neural canal. Holops, however, appears to have 

 had the sharp ridge margining the parietal bone which is seen in 

 the specimen figured by Biinzel. 



It is impossible to determine whether the parietal bone of Croco- 

 dilian character (figured by Biinzel, pi. i. figs. 1-2), is referable to 

 this species or to some other animal. Its distinctive features are the 

 sharp lateral ridges margining the temporal fossae, the fineness of 

 the circular pits on the bone, and the remarkable thinness of the 

 bony substance. 



That this species can remain in the genus Crocodilus is impro- 

 bable ; but at present I see no grounds on which to separate it. 



Pleueopeltus Suessii, Seeley. 



Postfrontal Bones of a Chelonian Skull. 



Two fragmentary bones (PI. XXVIII. figs. 8, 9), right and left, 

 present on their external surface impressions of scutes, and on their 

 under surface portions of a large cavity which I believe to be orbital ; 

 therefore I interpret these fragments as being postfrontal bones of a 

 large Chelonian of Emydian affinities ; and as the skull, when com- 

 plete, was obviously of large size, it may well have belonged 

 to the animal indicated by the large costal plates presently to 

 be described. The remarkable feature about this bone is the 

 character of its sutures ; for while a groove runs round the thin 

 margin in which the edge of the bone terminates, and evidently 

 received a sharp ridge from the adjacent bone, the margin on the 

 under side is bevelled, and thus demonstrates a union of the bones 

 by squamous overlap. The under surface of the bone (fig. 9) is crossed 

 by an oblique ridge, which divides it, as preserved, into two nearly 

 equal portions. This ridge helps to form a part of the posterior 

 boundary for the eye-ball, and is characteristic of Chelydra and 

 allied genera. The orbital surface is concave, and more resembles 

 that of Chelydra serpentina than that of Trachydoglossus ; and the 

 resemblance extends even to the position of the vascular foramen 

 at the back of the orbit, though there may, perhaps, in the fossil be 

 several small foramina in a line. This surface, as preserved, mea- 



