— 323 — 
small puboischiadic vacuity. The pelvis in general is strikingly si- 
milar to that of Palaeohatteria, and must be regarded as morpho- 
logically very primitive. 
Limbs. 
The limbs are closely similar to those of the South African form 
and of Stereosternum, and are so well illustrated in the plates that 
verbal description may well be brief. A comparison of the figures 
given by Gervais, Seeley, Broom, Woodward, Cope and Osborn will 
show that in the Mesosauridae the fore and hind limbs are of about 
equal size, as far as the mesopodials, the carpus and tarsus fully 
ossified (in the adult), but that the pes is very much larger than 
the manus. Another striking feature is that the arm, in nearly 
every case, extends straight outward or backward (cf. figures by 
Gervais, Seeley and Osborn, and Plate II. in the present paper), while 
the hind leg is almost always flexed at the knee (cf. figures of 
Cope, Osborn, Broom, A. S. Woodward, and Plates Il. and Il. in 
the present papers). 
Fore limb, 
The humerus, in so faras it differs at all from Stereosternum, 
seems to be relatively wider at its distal extremity. The ulnocon- 
dylar (entepicondylar) foramen is conspicuous, and in posterior view 
a radiocondylar (ectepicondylar) groove is visible. The head of the 
humerus is very simple and there is only the merest suggestion of 
a deltoid crest. 
The radius and ulna are of very nearly the same size, the radius 
very slightly the longer. Their proximal ends are closely apposed, 
but distally they are separated by some 5™"., embracing between 
them the intermedium. The elbow joint is of very simple character, 
suggesting that of the urodele amphibia. Comparison of the present 
material and the figures of the related forms given by Gervais, 
Seeley and Osborn show the elbow extended and the palm directed 
downward in nearly every well preserved example, justifying the 
conclusion that the elbow was capable of only very limited flexure 
and practically no torsion. The ratioof arm and fore-arm is almost 
exactly two to one. The carpus is fully ossified in the adult, but 
in an immature specimen only the proximal elements and the se- 
cond distal were ossified (In a half-grown Stereosternum figured by 
