380 



Annals of the South African J^Iuseum. 



a comparison with the Cape specimen is thus a little difficult. The 

 fore limb, the ribs, and vertebrae agree so closely in the two speci- 

 mens as to render it highly probable that the Cape specimen is the 

 adult of Giirich's type. The presence of two foramina in the 

 humerus of the type I am not inclined to regard as a normal 

 feature, and not improbably it is post-mortem. In the crushing 

 fossil bones are frequently altered and even have remarkable openings 

 made in them, e.g., Seeley's type of ? Cynognathus leptorhimis. 



The following are some of the principal measurements of the 

 bones of the best specimens :— 



Paris Type. 



Length of Humerus 25 mm. 



Eadius about 13 mm. 



12 mm. 

 4-5 mm. 



Ulna 



1st Metacarpal 



2nd 



3rd 



4th 



gth 



5*5 mm. 

 5' 8 mm. 

 5'5 mm. 

 -5 mm. 



Giirich's 

 Type. 



11 mm. 

 10 J mm. 



3 mm. 



5 mm. 



5 mm. 



5 mm. 



4i mm. 



Calvinia 

 Specimen. 

 24 mm. 

 12-8 mm. 

 12 mm. 



4*8 mm. 



5-6 mm. 



•5-5 mm. 



•5 '5 mm. 



4-3 mm. 



Capetown 

 Specimen. 

 27 mm. 

 14-8 mm. 

 14-2 mm. 



4-8 mm. 



6 '5 mm. 



6-8 mm. 



0-4 mm. 



5-2 mm. 



There appear to be thus three species of Mesosaurus known — M. 

 tenuidens, Gervais, represented by the Paris type, the Calvinia 

 specimen, and possibly also the Nieuwondtville specimen ; M. 

 capensis (Giirich), represented by Giirich's type and the specimen 

 described by Seeley ; and M. pleurogastcr, Seeley, very imperfectly 

 known. 



