mesosauria oe south africa. 587 



§ 2. The Kimberley specimens of Mesosaurus pletirogaster. 



Many years passed without further evidence of Mesosaurus. But 

 about 1878 Mr. G. H. Lee, F.E.M.S., of Kimberley, obtained from 

 the shale at the margin of the Kimberley Diamond Mine some 

 specimens, which were partially figured by Mr. J. W. Matthews in 

 his ' Incwadi Yami' in 1887. In 1878 these four specimens, which 

 were all that were collected, were deposited in the British Museum. 

 Two display the characters of the lower dorsal and lumbar vertebrae, 

 the dorsal ribs and abdominal ribs ; the third fragment shows some 

 characters of early caudal vertebraB, and the hind foot, which lies 

 towards them ; the fourth specimen belongs to the middle region 

 of the tail. There are slight differences in the relative sizes of 

 the bones in the several slabs, and differences in the colour and 

 hardness of the marly matrix, so that the remains may be portions 

 of more than one individual^ but I have no doubt that they are all 

 referable to one species. 



They show that Mesosaurus was a long-tailed reptile, with hind 

 limbs well developed. The remains are not easily compared with 

 the type in Paris, which is in a very dark hard matrix • but they 

 add materially to our knowledge of the genus, and are now described 

 under the numbers in the British Museum Catalogue. 



No. 1. — 49972. Presented by Wm. Benstead Smith, Esq., Regis- 

 trar of Kimberley Mine. This specimen, found | mile S.E. of Market 

 Square, Kimberley, in January 1878, is a natural mould in pale 

 whitish calcareous shale, from which the bones have disappeared. 

 The late Mr. Wm. Davies placed with it a plaster-of-Paris impression 

 which exhibits the forms of the bones in natural relief. It shows 

 the ventral aspect of the bodies of eleven vertebrse, eight of which 

 carry ribs ; the last three show no trace of ribs, and may therefore 

 be lumbar. 



The bodies of the vertebrae are not in close contact, but separated 

 by narrow intervertebral spaces. Each centrum is 6 millimetres 

 long. Its form is semicylindrical, being convex from side to side, 

 without the slightest concavity in length. On the contrary, the 

 articular faces are a little contracted, and, on the evidence of one dis- 

 placed centrum, are characterized by a subconical articular cavity 

 penetrating into the centrum for fully a third of its length. The 

 neural canal is wide, concave below, and angular above. The inter- 

 vertebral perforations for the nerves are inferior in position to the 

 transverse tubercles from the neural arch. These tubercles increase 

 the width of the vertebrae, as exposed, to about 1 centimetre. 



The ribs, 4 centimetres long, are strongly curved in the proximal 

 part, and less curved distally, where they become cylindrical and 

 thicker, being fully 3 millimetres wide. In the proximal third the 

 rib is less than 2 millimetres thick, so that it is there flattened from 

 below upward ; and its small articular extremity bends a little 

 forward. The measurement over the two extremities of the dorsal 

 ribs is 3 centimetres. The length of the posterior ribs diminishes, 

 so that the last is only 1-5 centimetre long, and the distal ends of 



aJ.G.S, i\o. 192. 2 s 



