ON A NEW SPECIES OF PLESIOSAURUS 



2. In the Tekosauria (J^eleosaurus temporalis) there is a singular 

 aperture closel}' resembling in form and position the external nostril 

 of the Plesiosaiirus, though in the Tekosauria there is every reason 

 to believe that the nostrils were, as in the Gavials, at the end of the 

 snout. The bony margins of the aperture are, however, somewhat 

 differently constituted in the two genera. 



3. In the Teleosauriis the jugal bone is long and slender. In 

 Plesiosaitrjts Etheridgii and others, I find a bony style of greater or 

 less length, broken posteriorly, but having otherwise precisely the 

 same relations and form as the jugal of the Teleosauriis} This pro- 

 cess is particularl}' well shown in a cranium (named P. dolichodeirus) 

 in the Museum of the Society, and is figured by Mr. Conybeare in his 

 restoration. 



4. Contrary to what is commonly stated, the post-frontal appears 

 to me, in P. Etheridgii and Hawkinsii at any rate, to articulate with 

 a bone, the homologue of the squamosal ^ of the Crocodile. 



5. The squamosal of the Plesiosaurus seems to have been con- 

 founded by some with a process of the parietal. 



6. The temporal fossa is divided by the post-frontal in the manner 

 so characteristic of, though not absolutely peculiar to, the Crocodilian 

 reptiles. The great superior fossae correspond with the large superior 

 temporal fossae of the Teleosaurian, and even the narrowness and 

 crested form of the upper surface of the parietal (supposed to be 

 distinctive of the Plesiosaurus) are very closely approached in such 

 Teleosauria as T. temporalis. 



7. The exoccipital sends outwards and downwards a process which 

 reaches the great quadratum, and between this below, the quadratum 

 externally, and the squamosal above, there is a large aperture in the 

 Plesiosaurus. 



In the triassic Eiialiosauria, however, the corresponding interval 

 is, judging by Hermann von Meyer's figures of Nothosatiriis, smaller 

 in proportion, or, as in Simosaurus, absent (?). On the other hand, it 

 is larger in the Teleosauria than in the existing Crocodilia. 



8. The basi-sphenoid appears upon the base of the skull for a 

 great space in the Plesiosaurus, while in the ordinary Crocodile it is 

 not visible at all, being hidden by the pterygoids. Even in the 

 Gavial, however, the basi-sphenoid shows itself fully on the base of 

 the skull, while in the Teleosaitrus it is as much exposed as in the 



^ Hermann von Meyer figures a very .similar process in Simosaurus, pi. 65, figs, i & 2. 



- This is the bone commonly but erroneously termed the "mastoid" in the Crocodile. 

 Rathke and Hallman have long since satisfactorily shown that the homologous bone has no 

 relation with the true mastoid. 



