CETPTOCLEIDUS OXONIENSIS. 183 



surface of contact with the intermedium. In one case (a.o., text-fig. 91, A) it articulated 

 externally by a short facet with a peculiar phalange-like bone lying on the preaxial 

 side of the radiale (^a prepollex). 



The ulna is much smaller than the radius ; its humeral facet is gently convex, its 

 inner (radial) surface is likewise convex, while distally it bears two flat facets making 

 an obtuse angle with one another, for the intermedium and ulnare. 



The proximal row of carpals consists essentially of the radiale, intermedium, and 

 ulnare, but in many specimens there is a tendency to develop accessory ossicles on the 

 preaxial or postaxial border or on both, and there is considerable variation in the form 

 and manner of development of these accessory ossicles. In some cases it seems as if 

 the increased width of the radiale and ulnare, consequent upon the expansion of the 

 paddle, led to a tendency to ossify from more than one centre, and this may bring about 

 the total or partial separation of the preaxial portion of the radiale and the postaxial 

 part of the ulnare (text-fig. 90, C) ; often there is a want of symmetry in the paddles of 

 opposite sides. In some cases it seems as if instead of a separation of the ulnare 

 into two elements there has been a fusion with an originally distinct element 

 (text-fig. 91, A, a.o.) corresponding to the bone called the pisiform in some of the 

 paddles described above (e. g., Tricleidus, text-fig. 77, p. 160). The intermedium 

 articulates mainly with the ulna, the facet for the radius being small and perhaps in 

 some cases absent. 



The distal carpals are three in number, the first (preaxial) articulating with the 

 radiale (and anterior accessory ossicle if present), the second with the radiale and 

 intermedium, the third (postaxial) with the intermedium and ulnare, while its postaxial 

 border may have a facet at its proximal end for contact with the fifth metacarpal (text- 

 fig. 91, A), which, as usual, articulates directly with the ulnare. The first metacarpal, 

 which is flattened like the carpals, articulates only with the first distal carpal ; 

 the second metacarpal, which is cylindrical, Avith the second carpal ; the third has 

 two facets, one for the second the other for the third carpal, with Avhich also the 

 fourth metacarpal articulates ; the fifth metacarpal has already been referred to. 

 The phalanges are cylindrical and somewhat constricted in the middle; the faces 

 by which they articulate with one another are nearly flat. The number of phalanges 

 in the difierent digits is not known. 



Pelvis (PI. X. figs. 3, 3 «, 3 i ; text-fig. 92). — The structure of the pelvis in this 

 species has been described in some detail in Geol. Mag. [4] vol. iii. p. 145. It is 

 composed of the usual three pairs of bones. The 'pxibis {pu., PI. X. figs. 3, 3 c, 3 h) is 

 relatively much wider from side to side and shorter from before backwards than is the 

 case with the pubis of Muroenosaurus {cf. text-fig. 65, p. 116). The anterior convex 

 border is thin, except at its outer angle, where it is thickened and produced into a 

 short process (a.e.a), separated by a notch from the median part of the border. This 

 antero-external process of the pubis is also present in Marcenosaurus, though less 



