Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/845

 and the proximal halves of the right femur and humerus, with the smaller paddle-bones, already mentioned, of this Plesiosaurus.

Mr. Mansel has recently seen these humeri and femora since their restoration ; and he has identified them as the limb -bones which he exhumed together with the spinal column which he sent me. Their general facies, the peculiar texture of their surface, and the correspondence of small pieces of the clay still adhering to them, confirm Mr. Mansel's statement that these limb-bones did belong to the same individual. I may add that there is a close resemblance in these points between the paddle-bones and the large flat bones of the pelvic and breast-girdles. I have entered into these details because, on account of the remarkable construction of the paddles, it is important that their identification with one another and with the spinal column should be as complete as possible.

Spinal Column. — The spinal column is that of a long-necked Plesiosaurus. All the early cervical vertebrae have been subjected to lateral pressure, which has flattened the sides of the centra, and reduced their breadth, but increased their height. Throughout the spinal column the neurapophyses have been broken off from the centra, to which they were completely anchylosed ; and very few of them have been recovered. The eighty-six vertebrae which have been preserved are distributed as follows. Twenty-seven bear a transverse process low on the side of the centrum, and therefore belong to the front of the neck. Their combined lengths amount to nearly 5 feet ; but the original length of this part of the neck was more than this, because several vertebrae behind the axis are certainly wanting, and there is another gap between the 12th and 13th of the series. Twenty-three have the transverse process replaced by a costal pit, higher on the side of the centrum, or they have a transverse process rising from the centrum into the root of the neurapophysis. These, then, are transitional vertebrae between the front of the neck and the trunk, or between the dorsal and caudal segments. I am not acquainted with criteria by which the transitional centra of these regions can be certainly distinguished, the prethoracic and early thoracic from the lumbar ones. The larger ones I have assigned to the lumbar region, because their dimensions accord best with those of the early caudal centra. The united lengths of the transitional vertebrae amount to nearly 4 feet.

Nineteen have the transverse process borne wholly on the neurapophysis, and are reckoned dorsal or mid-trunk vertebrae. Their united lengths give 3 feet 6 inches.

Seventeen are caudals, all but the foremost bearing chevron-facets. Their combined length is 2 feet 6 inches. The united lengths of all the vertebrae make about 15 feet ; and taking into account the known large gaps in the neck, and the probability that other vertebrae are also missing, the original length of the spinal column will probably be not overestimated at 17 feet.

The atlas and axis are anchylosed. A shallow vertical groove on their side indicates their original separateness. The anterior articular face of the atlas is a cup with a diameter of about 1.1 in., but