212 



THE EXTINCT BATRACHIA, REPTILIA 



face, in front by the vomers, behind by the nares and palatine bones. They terminate in 

 a' narrow process behind, whose extremity is broken in the specimen at my disposal, but 

 which is too slight to have supported a malar arch, unless it were as in the Dolphins. 

 Each maxillary bears seventeen sub-equal teeth. The nostrils are linear and superior, as 

 in Mosasaurus, and if separated by a septum, it was exceedingly slender. A portion of it 

 has been preserved; it appears to be composed of co-ossified nasal and frontal bones. The 

 nares extend to a point as far in advance of the anterior margin of the orbit, as the latter is 

 in advance of the posterior margin of the post-orbitals. The prefrontal* are largely devel- 

 oped and margin the posterior part of the nares. Their posterior exterior margin projects 

 strongly in the plane of the muzzle, and has caused the orbit to be horizontal, and the 

 range of vision vertical, as in some aquatic serpents. 



The froutal is a, wedge-shaped flat bone. The post frontals are large, flat and promi- 

 nent, and project beyond the process they send posteriorly to join the squamosal. Pos- 

 teriorly it embraces a broad rectangular process of the parietal, which contains near its 

 front suture, the parietal fontanolle. The projection is considerably wider than as repre- 

 sented by Ooldfuss in the genns Mosasaurus. 



The parietal has two broad lateral wings, which advance on the frontal, and form pos- 

 teriorly the broad anterior margin of the temporal fossa. The parietal crests are separ- 

 ated by a plane which is narrowed posteriorly. Two antero-superior projections of the; 

 supraoecipital embrace; it on each side below the crest, while: it is overlapped just below, 

 by the anterior extremity of the prootic; this does not extend so far forwards as the su- 

 praoecipital. In front of, and below this point, the parietal is decurved, and forms a, con- 

 siderable part of the lateral wall of the cranium; though with but moderate antero-pos- 

 terior extent. The plate, as preserved on one side of the specimen, has extended to the 

 body of the sphenoid, where extensive sutural surface has received it, I can find no suture 

 crossing it, and it is apparently all alisphenoid or all parietal. I incline to the former 

 view, for where it is separated at its superior base from the parietal, the appearance is 

 quite as similar to suture as fracture. A part of the parietal is, however, undoubtedly de- 

 curved in front of it. The structure is quite as Crocodilian as Ophidian in this point. 



The anterior ala of the prootic overlaps this alisphenoid largely. Its posterior lamina. 

 does not quite meet the expansion of the exoccipital on the upper face of the suspenso- 

 rium, as it does in Mosasaurus. Inferiorly it is contact with outer and posterior base of 

 the sphenoid. 



The impraoceipital is somewhat crushed; it is slightly roof-shaped, but not so much so 

 as in M. missuriensis, nor so much below the plane of the parietals as in that genus. The 

 posterior extremity of the parietal appears to rest upon it without sending arches to the 

 opisthotic. 



