MESOSATJEIA OF SOUTH AFEICA. 597 



an elongated slender cylindrical form. The cervical ribs in the 

 Cape Town fossil are long and slender, and directed backward, close 

 to the vertebrae ; in the Paris specimen the cervical ribs have been 

 figured with a considerable lateral expansion, which, however, is not 

 present.^ The shoulder-girdle is at first sight very dissimilar, but a 

 mass of matrix appears to cover the hinder part of the coracoid 

 plate in the Paris fossil and to hide the posterior emargination of 

 the bone. The lateral pre-acetabular expansion seen in the Paris 

 fossil is absent from the Cape Town specimen, but it may possibly 

 be lost upon the upper slab. The humerus in the Paris specimen is 

 more compressed distally and the foramen is longer. The evidence 

 is insufiicient to prove specific distinction. 



§ 4. The Mesosauetjs i^ the Albaisty Museum. 



Another specimen of apparently the same genus, from near 

 Burghersdorp, is contained in the Albany Museum at Graham stown. 

 It shows the dorsal aspect of dorsal vertebras and ribs. The vertebrae 

 are no wider than in the Cape Town fossil, but relatively longer. 

 While in the latter seven vertebrae occupy a length of 4| centimetres, 

 in this only five vertebrae are contained in that length, but the ver- 

 tebrae are less closely articulated. The ribs are fully | centimetre in 

 diameter, so that the interspaces between them are only half as wide 

 as the ribs. As they are preserved, inclined backward at an angle o£ 

 45°, they lie in close contact distally on the right side and overlap 

 on the left side. They appear to be a little ovate in section, 

 being wider than deep, so that this character is not peculiar to 

 Ditrochosaurus. The proximal ends are compressed and recurved. 

 They have a length of about 4^ centimetres ; and the transverse 

 measurement over the bodv as preserved is 7 centimetres. They 

 lie in natural connexion with the vertebrae. On the left side of the 

 sixth vertebra, the cast shows an impress as of a flat transverse process. 

 Apparently the anterior edge of the rib is in close contact with the 

 concave posterior margin of the process. The contact is as close 

 as though this relation were articular. 



Thirteen vertebrae are preserved in the cast, with indications of 

 one more at' each end, imperfectly preserved, and on the left side 

 there are thirteen ribs in sequence. The vertebrae seen from above 

 are transversely oblong. They are narrowest in front, widest in 

 the middle, and narrow again posteriorly. The greatest transverse 

 measurement is 1^ centimetre. The antero-posterior measurement 

 increases a little from front to back, being less than | centimetre 

 anteriorly, and more posteriorly. The neural spines are compressed 

 from side to side, moderately elevated, higher than in the impression 

 from the cast, stronger behind than in front, and stronger in the later 

 than in the earlier vertebrae. On each side of the neural spine the 

 surface is convex from front to back and concave from side to side, 



^ I am indebted to Prof, Gaudry for evidence that the cervical ribs in the 

 tyY^e oi Mesosaicrus tenuidens are essentially the same as in this fo?sil. The 

 tenth vertebra of the type appears to have ribs with two distinct articular sur- 

 faces, and such ribs may be present in the ninth vertebra. 



