Observations on the Structure of Mesosaurus. 107 



The impression formed by the mandible is sufficiently satisfactory to 

 enable one to make out the dentary, splenial, and angular bones. 

 Of the palate the impression is much less satisfactory. Seeley 

 speaks of the palate as being " completely closed," and considers it 

 as "possible that the palato-nares may be in the depression behind 

 the posterior divergence of the pterygoid bones." The only palatal 

 bones of which there are any impressions in the specimen are no 

 doubt the pterygoids as Seeley recognised. But so far as shown in 

 the impression they are thoroughly Ehynchocephalian in type, 

 though greatly elongated, and there seems to be no good reason for 

 regarding the internal nares as being situated behind them. 



In the basisphenoid region the elements are hopelessly crushed 

 and displaced. 



The cervical ribs are apparently all single-headed. 



The shoulder girdle is fairly well preserved, but it is crushed and 

 evidently considerably displaced. As the girdle is unlike that of 

 any other known animal, it is impossible to speak with any degree 

 of confidence of the original condition of the elements. In the 

 specimen there are two fan-shaped portions of the girdle which 

 approach each other in the middle line. These are regarded by 

 Seeley as portions of the coracoids, the rest of the coracoids being 

 directed outwards ^and- backwards. The portion which is directed 

 forwards and outwards beyond the foramen is believed to be the 

 scapula. In fig. 2 I have attempted a restoration of the girdle. 

 The fan-shaped part I believe to be the precoracoid, the posterior 

 part the coracoid, and the anterior the scapula. In the specimen I 

 consider both arches have been displaced by the coracoids having 

 been drawn outwards. Although I have been unable to find any 

 sutures, indications seem to be given of the different elements by 

 the radiations of the bony fibres. In front of the cartilage bones 

 there are evidences of an interclavicle and of the two clavicles. As 

 these are considerably crushed it is difficult to be at all sure of the 

 original condition. I can find no evidence of the interclavicle 

 having had a posterior median process. If the interpretation of the 

 elements here given should prove correct, then it would appear that 

 the type of girdle in Mesosaurus is a modification of the type found 

 in Procolojphon. 



It is remarkable that in the Cape Town specimen, though the 

 impression is of the ventral surface, there are only the indications of 

 three or four of the abdominal riblets. 



It is somewhat difficult to decide with certainty the species 

 of this specimen. It certainly differs greatly from the figure of 

 the Paris specimen, and the question depends on what reliance can 



