18 
FOSSIL REPTILIA OF THE 
more rapid convergence of the sides of the upper jaw to the more pointed muzzle. 
The temporal fossee may appear broader than natural in this crushed skull, but with 
due allowance this shape was square, not oblong, as in Plesiosaurus homalospondylus. 
The intervening parieto-frontal crest is relatively longer, and we may infer that the 
biting muscles were larger and more powerful in relation to the more massive propor- 
tions of the dentigerous parts of the jaws \\\ Plesiosaurus homalospond^lus : the orbits 
are relatively less ; their antero-posterior diameter is less than one fifth of the same 
diameter of the skull taken from the back part of the parietal (7) in PI. homalospondplus ; 
it is more than one fifth in PI. dolichodeiriis ; the orbits are equidistant from the two 
extremes of this diameter in PI. liomalospondylus ; they are nearer the back part of the 
head in PI. doliclodeirus. In PI. rostratus (Tab. IX) the temporal fossae present some- 
what intermediate proportions between those in the two foregoing species ; but the 
rostral production of the maxillary part of the skull sufficiently distinguishes the 
cranium of PI. rostratus from that of previously known species in a comparison of 
detached skulls ; whilst its greater relative size to the body more especially distin- 
guishes it from that in PI. Itovialosptondylus or PI. dolichodeirus. 
In PI. llaiolcinsii-'^ the longitudinal diameter of the temporal fossa exceeds the 
transverse diameter, but not in so great a degree as PI. liomalospondylus, and the upper 
jaw is relatively narrower than in that species. This is also the case in PI. macro- 
cep>lialus,\ in which there is a more marked constriction of that part, anterior to the 
orbits, showing a tendency to the “ rostral ” character, which is exaggerated in PI. 
rostratus. 
Pectoral and pelvic arches and limbs (Tabs. V and VIII). 
Of the limbs only the humeri and femora have been preserved in the skeleton 
(Tab. V) ; these bones show the usual form, with their respective characteristic modi- 
fications, as exemplified in the different contour of the anterior border, which is 
straight or partly convex in the humerus, and is concave in the femur. The length of 
the humerus is 12 inches, that of the femur 13 inches; the distal breadth is nearly 
the same in both, namely, 6 inches. In the right femur, the coarse fibrous texture 
which pervades the whole thickness of the bone is exposed. A portion of the exten- 
sive scapulo-coracoid arch comes into view from beneath the anterior dorsals on the 
right side (Tab. V, 52 ). The ilium (ib., 62) presents the usual form; straight, slender 
at its proximate end, with a slightly twisted, subcylindrical shaft, expanding to a 
breadth of nearly three inches at its acetabular end. The entire length of the 
* ‘Geol. Trans.,’ 2nd series, vol. v, pi. 45. 
t Ibid. 
