586 PROr. H. G. SEELEY ON THE 



44. The Mesosatjeia of South Africa. By H. G. Seeley, Esq., 

 F.R.S., F.L.S., F.G.S., Professor of Geography and Lecturer in 

 Geology in King's College, London. (Eead June 22nd, 1892.) 



[Plate XVIII.] 



Contents. p 



§ 1. Introduction 586 



I 2. The Kimberley specimens of Mesosaurus pleurogaster 687 



§ 3. The Mesosaurus tenuidens (Gervais) from Albania 591 



I 4. The Mesosaurus in the Albany Museum 597 



I 5. The Eelations of Mesosaurus with Stereosternum 598 



I 6. Classification of the Mesosauria 604 



§ 1. Inteodtjctiobt. 



Prof. Gervais in 1865 described under the name Mesosaurus tenui- 

 dens the remains of a small reptile from Griqualand, South Africa, 

 which had been brought to Prance more than thirty years before. 

 It is preserved in a slab which shows the skull and anterior portion 

 of the skeleton. As with other vertebrate remains from South 

 Africa, its exact geological age is unknown. The author states ^ 

 that the animal was a little larger than the Ocellated Lizard, and 

 has many affinities ; resembling in some characters terrestrial types 

 of reptiles, while in other characters it approaches Simosaurians and 

 Plesiosaurians. Its cervical vertebrae have some resemblance to 

 those of Crocodiles. The lower jaw recalls in a general way Croco- 

 diles and Plesiosaurs. The dorsal vertebrae are rather elongated 

 and comparable to those of Homoeosaurians and of Teleosaurs. The 

 ribs are stronger than in any known reptile except Pachypleura^ 

 and are arranged as in that genus. They have much the same rela- 

 tion to the ribs of other reptiles that the ribs of Sirenians have to 

 those of other mammals. The sternal ribs, identified by Cope, were 

 regarded as annelid tracks. The scapular arch is compared to those 

 of Crocodiles and Plesiosaurs ; but the scapula and coracoid are 

 anchylosed. The humerus is that of a Plesiosaur or Simosaur, with 

 an ent-epicondylar perforation, like that seen in Var.anus and 

 certain mammals. The forearm and hand are of less aquatic type 

 than in Plesiosaurs, and approach the terrestrial type ; but the ulna, 

 unlike that of terrestrial reptiles, has no olecranon. The animal is 

 compared to Lariosaurus, MacJirimosaurus, and Paehypleura, but is 

 distinguished from them by the form of the head, the teeth (which 

 are exceptionally long), and the number of cervical vertebrae, which 

 were stated to be seven, with two which are intermediate in cha- 

 racter between the cervical and dorsal. 



^ Gervais, ' Zoologie et Paleontologie Generales,' 1867-69, p. 223, pi. xlii. 



