RHINOCHELYS. 175 



Podocnemis, that there can be but little hesitation in 

 referring it to the same family. 

 Transferred from the Museum of Practiced Geology, 1881. 



Family Position Uncertain. 



The undermentioned genus is definitely known only by the skull, 

 and its serial position must remain uncertain till either the com- 

 plete shell is known or until we gain definite knowledge of the 

 skull of the PlesiocJielyidce. On account of the presence of distinct 

 nasals and the meeting of the palatines in the middle line, the 

 genus has been provisionally referred by the writer * to the Pleuro- 

 dira. This reference is confirmed by the characters of the humerus 

 No. R. 402 (p. 175). The Portlandian skull, to which the name 

 Stegoclielys 2 has been provisionally applied, differs from that of 

 Rhinochelys by the median union of the prefrontals, the incomplete 

 temporal roof, and the emargination of the lower border of the in- 

 ferior temporal arcade. A large number of specific names were 

 applied by Seeley 3 to crania of Rliinochelys in the Cambridge 

 Museum ; but since these are unaccompanied by any description, 

 they can only rank as MS. ones. If rightly referred to the Pleuro- 

 dira, the skull of BhinocJielys shows an approximation to the 

 Cryptodiran type. 



Genus RHINOCHELYS, Seeley 4 . 



Skull ^with the temporal fossae completely roofed over, after the 

 manner of the Clitlonidce, a post-temporal (parieto-squamosal) bar 

 being probably present, in some cases at least ; pterygoids narrow 

 and emarginate ; palatines meeting in the middle line ; vomer 5 

 dividing posterior nares and connecting palatiucs with premaxilhe. 

 Distinct nasals ; prefrontals separated by nasals and frontals ; jugal 

 continuing line of alveolar border of maxilla to tympanum ; quadrato- 

 jugal entering into formation of tympanic ring, which appears to 

 have been notched inferiorly. Palate with a ridge on either side of 

 oral surface; mandible with the interdentary suture obliterated, 

 and a prominent oral ridge. 



1 Quart. Journ. Geol. Soc. vol. xlv. p. 227 (1889). 



2 Ibid. p. 229.^ See Addenda. 



3 Index to Aves &c. in Cambridge Museum, pp. xviii, xix (1869). 



4 Op. ciVj). 25 (1869). 



5 Teste Seeley. See also Quart. Journ. Geol. Soc. vol. xlv. p. 228. 



