No. I.] THE SKULL LV THE MOSASAURID^. 7 



8. The mandible is composed of all the elements character- 

 istic of reptiles : the articular and surangular distinct ; the angu- 

 lar represented by its anterior portion only ; and the corononoid 

 present. 



After this a full description of the skull is given. 



The nasals are said to be co-ossified with the frontals. " The 

 parietal is decurved, and forms a considerable part of the lateral 

 wall of the cranium, though with but moderate antero-posterior 

 extent. The lateral wall extends 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. A part of the parietal is, however, undoubtedly de- 

 curved in front of the alisphenoid. The structure is quite as 

 crocodilian as ophidian in this point." — "The anterior ala of the 

 pro-otic overlaps the alisphenoid largely. Its posterior lamina 

 may or may not meet the expansion of the exoccipital on the 

 upper face of the suspensorium. Inferiorly, it is in contact 

 with the outer and posterior face of the sphenoid." — "The 

 opisthotic stands obliquely upward and forward, and furnishes a 

 glenoid cavity for the articulation of the quadratum. It has a 

 process, directed upward and forward, which occupies a con- 

 cavity on the inner face of the squamosal, which has the same 

 direction." — " The presphenoid appears to have been distinct. 

 Its base was small ; it is readily lost, and I have not seen it." — 

 " The vomer is divided, and is composed of two slender, com- 

 pressed bones in contact." The posterior wing of the true 

 pterygoids is considered the pterygoid, the anterior toothed part 

 the palatine. The lower jaw is fully described. 



Owen} 1877. 



The foregoing paper of Professor Cope was strongly criticised 

 by Professor Owen. Professor Cope^ answered these criti- 

 cisms in 1878, and it is best to consider the different opinions 

 . together. 



Professor Owen shows very clearly that the so-called Ophidian 

 characters of the Mosasauridae do not exist in the skull ; that 



1 Owen, Professor, On the Rank and Affinities in the Reptilian Class of the Mos- 

 asauridce, Gervais. Quart. Journ. Geol. Soc, November, 1877, pp. 682-715. 



2 Cope, E. D., Professor Owen on the Pythonomorpha, Bull. U. St. Geol. and 

 Geogr. Surv. Terr., Vol. IV, No. i, Washington, 1878, pp. 299-311. 



