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OBSEBVATIONS ON THE STBUCTUBE OF 



MESOSAUBUS. 



By E. Broom, M.D., B.Sc, C.M.Z.S. 



(Bead June 29, 1904.) 



Plate IX. 



The genus Mesosaurus was founded by Gervais in 1865 for a small 

 fossil reptile found in Griqualand West, South Africa. The type 

 specimen, which is now in Paris, consists of the head, neck, the two 

 fore limbs, and the greater part of the body, and has been named 

 Mesosaurus tenuidens. 



In 1889 Giirich described, under the name Ditrochosaurus capensis, 

 the remains of reptile closely resembling Mesosaurus, from near 

 Hopetown. The remains are evidently those of an immature animal, 

 and there seems little doubt that they are those of a young 

 Mesosaurus. 



In 1892 Seeley described a number of imperfect remains of 

 Mesosaurus in the British Museum, and also the very fine specimen 

 belonging to the South African Museum. The Cape Town specimen 

 he regarded as belonging to the type species, but the British Museum 

 specimens he referred to a new species, M. pleurog aster. * From, 

 these specimens he was able to add much to our knowledge of 

 the genus. The Cape Town specimen shows the neck, .dorsal 

 vertebrse and ribs, and the fore limbs in an almost perfect state of 

 preservation, and less satisfactorily the shoulder girdle, which is 

 considerably crushed and displaced. The London specimens reveal 

 something of the structure of the abdominal ribs, and one of them 

 shows the structure of the hind foot. 



Though no further specimens of Mesosaurus have been described, 

 a considerable number of specimens of the closely allied South 

 American genus Stereo sternum have been described, and almost 



