106 Transactions of the South African Philosophical Society. 



The first three caudal vertebrae have each fairly long pointed ribs. 

 Those of the first two are directed outwards ; that of the third curves 

 slightly backwards. In the fourth caudal the ribs are slightly 

 shorter, but also curve slightly backwards. In the case of this 

 vertebra there is an appearance suggestive of an intercentrum, but 

 the evidence is not very satisfactory. From the fifth to the ninth 

 vertebrae the caudal ribs steadily decrease in size. The ribs of the 

 fifth and sixth vertebrae are directed outwards ; those of the seventh, 

 eighth, and ninth point slightly forwards. The sixth vertebra 

 shows facets for a chevron bone. The tenth, eleventh, and twelfth 

 vertebrae are too imperfectly preserved to admit of description. 

 From the thirteenth to the twentieth the vertebrae are represented 

 by imperfect casts of the right sides. These vertebrae agree fairly 

 closely one with the other. They have large arches and spinous 

 processes, and are remarkable for having w T ell-marked splitting 

 planes. One chevron is seen in almost perfect condition, and is 

 strikingly like the chevrons of Stereo sternum. The side view of the 

 seventeenth caudal vertebra is shown in fig. 6. A restoration of 

 the lower surface of the pelvis is given in fig. 4, while fig. 5 shows a 

 restoration of the tarsus and metatarsus and phalanges. 



From immediately in front of the pelvis to near the anterior end 

 of the specimen there are the impressions of a very large number of 

 delicate abdominal ribs. These are so slender that with the 

 crushing each appears to have been broken into many fragments. 

 It is seen that there has been a median series with on each side 

 certainly two and possibly, but not probably, three lateral series. 

 There would appear to have been about four sets of splints to each 

 vertebra. The riblets are much more slender than those figured by 

 Seeley. in M. pleurog aster. .. * ; .:. , . :...: .. . .::„ ..: ::■ ' ■;..: 



With regard to the species of this specimen, it is at present' 

 impossible to speak with certainty. So far as the vertebrae and ribs 

 are concerned I fail to detect any differences of importance between it 

 and the Cape Town specimen. If Seeley is correct in regarding the 

 Cape Town specimen as belonging to the type species, then this 

 specimen is probably also Mesosaurus tenuidens. 



Notes on the Cape Town Specimen. 



This specimen has already been fully described by Prof. Seeley, 

 and a satisfactory figure has been given. There are still, how- 

 ever, one or two points on which further observations may not be 

 superfluous. 



The head is represented by the impression of the under surface. 



