Description of a New Plesiosaur. 321 



approach very nearly to those of some of the vertebrae here described. 

 In both cases also there is a sharp haemapophysial ridge with a con- 

 cavity on each side, and the articular surface is strongly concave 

 with a sudden depression in the middle ; this last character is more 

 strongly marked in the present species. The neural spines in 

 Plcsiosaurus valdensis also resemble those of the present species, 

 being rather low and curved backwards (see Lydekker, Catal. Foss. 

 Eept. Brit. Mus., pt. ii., p. 188, fig. 61). There are, however, a 

 number of differences in detail which seem to render it impossible 

 that our specimen is specifically identical with this species. 



Comparison of the proportions of the cervical vertebrae of different 

 species of Plesiosaurs is only of value in a very general way since 

 the vertebrae have been, for the most part, found isolated or in small 

 groups, so that their position in the neck is usually uncertain, and 

 they may have belonged to animals of different sizes. Nevertheless, 

 on the whole it may be taken as fairly certain that Plesiosaurus 

 capensis is a member of the group of small Plesiosaurs which in 

 Europe is represented by P. degenliardti and P. valdensis from 

 the Wealden, and perhaps by P. bcrnhardi from the Cambridge 

 Greensand. 



The occurrence of a Plesiosaur in South Africa is of peculiar 

 interest since it is not improbable that the group may have been 

 derived from some form related to the Therocephalia remains of 

 which are found on the Permian of that region. 



The approximate dimensions (in centimetres) of the type specimen 

 of Plesiosaurus capensis are : 



SKULL. 



Length from tip of snout to occipital condyle 27 7 



Length from tip of snout to hinder point of quadrate 32'6 



Length from tip of snout to vertex 29-3 



Length from tip of snout to external narial opening 10-4 



Width between outer angles of quadrates 18-3 



Width of snout where the maxillo-premaxillary suture crosses the alveolar 



border 5-8 



VERTEBRA. 



Cervicals. Dorsals. 

 A. 



Length of centrum in mid-ventral line 1'9 2-1 2-5* 3-2 2-8 



Width of posterior articular face .. .. 30 3-3 (app.) 3-6 5*0 (upp.) 4-6 



Height of articular face 2-5 2-7 (app.) 3-1 4-1 4-1 



United length of the two figured (text-Fig. 2) posterior cervical vertebra . . 7*0 



Height to top of neural spine of posterior cervical vertebrae 11-1 



* Vertebra figured PI. XVIII., fig. 6. 



