Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/852

 closely resemble those of this Kimmeridge Plesiosauinis ; and the points of similarity are just those wherein this departs from the Liassic types.

I find, on comparing them, a very close general and particular agreement between the humerus and femur of the Kimmeridge Plesiosaurus and two type specimens in the British Museum, labelled " No. 31,795. Femur, Plesiosaurus trochanterius, Owen," and "No. 31,787, femur of Plesiosaurus brachydeirus, Owen." No. 31,795 is smaller than the Kimmeridge humerus, but in all other respects closely resembles it. It has the same general form, arti- cular caput, trochanter and separating groove, and the rough warty muscular impression on the ventral surface and postaxial border. The preaxial and first postaxial segments of the distal border are inclined at a similar angle ; the preaxial segment is similarly con- cave. The remainder of this and the distal part of the postaxial border, including the wing, are unfortunately wanting, so that the comparison cannot be completed.

The Kimmeridge Plesiosaur's femur is extremely like No. 31,787, a femur of " Plesiosaurus brachydeirus, 0.," a longer bone (from a larger individual?), but Avith outlines which, so far as they are pre- served, closely resemble those of the Kimmeridge Plesiosaurus. At first sight most striking differences are a greater axial symmetry due to the smaller size of the wing, and the subdivision of the distal end into two facets only : but it only requires a second glance to see that the distal third of the postaxial border, with the corre- sponding part of the wing and of the distal border, have been broken off, and the rough fractured edge smoothed with plaster of Paris. It has a similar articular caput, separated by a groove running between the preaxial and postaxial borders from a strongly formed trochanter. The preaxial and so much as remains of the postaxial division of the distal end are inclined at a like angle, and each is similarly concave.

"When the comparison is extended to the second and third seg- ments of the limb, similar resemblances are apparent. The paddles available for this purpose are two — the well-known enormous paddle of Pliosaurus grandis, presented to the Dorchester Museum by its discoverer and restorer, Mr. J. C. Mansel, and the small paddle of Pliosaurus portlandicus in the British Museum, described and figured by Professor Owen in the Pabeonfcographical Society's Me- moirs, vol. xxii.*

In both these we notice the same formal indifferentism of the bones composing the cnemion and tarsus, and the same transverse extension of the tibia and fibula. In the Dorchester paddle, an excel- lent cast of which is in the north gallery of the British Museum, the femur is mutilated. It manifestly wants a great part of the wing, which has been split off by a straight fracture parallel to the axis running from the postaxial to the distal border. The tibia and fibula support flat multiangular tarsals, which are succeeded by five (Paleontogr. Soc. Mem. toL xxii. for 1868), pi. 4. fig. 1.
 * Fossil Beptilia of the Kimmeridge Clay, genus Plesiosaurus, by Prof. Owen