Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/506

 upper surface falls gradually from the proximal end, rises slightly over the shaft, and then again gently declines along e upper intercondyloid groove.

Remarks. — The general configuration of this bone (particularly the form of its extremities, and especially that of its proximal one) proves it to be reptilian, and at the same time separates it from the Enaliosauria, the remains of which are so common in the Kimmeridge clay of the Dorset coast.

A comparison of it with several humeri and femora of recent crocodiles and lizards leaves no doubt in my mind that it is the left humerus of a crocodilian ; but its axis is less twisted and its proximal end has a smaller upward curve than the humerus of now living crocodiles, from which it also differs in its enormous size. This last character also removes it from the extinct Crocodilia, the Teleosaurs and Stenosaurs, from Goniopholis and Poikilopleuron, none of which, so far as they are yet known to us, had humeri approaching the magnitude of this bone. There are three genera to the individuals of which a stature correlative with the size of this Kimmeridge humerus has been assigned — Streptospondylus, Cetiosarus, and Polyptychodon. Not anything, so far as I can learn, seem to be known of the limb-bones of Streptospondylus major, Owen; but those of Polyptychodon and Cetiosaurus are described as having a coarse spongy texture, and as being destitute of a medullary cavity.

The evidence on which these statements rest, so far as it has been accessible to me, does not appear to my mind to be decisive regarding these two points. The portions of long bones referred by the late Dr. Mantell to Cetiosaurus, formerly in his cabinet, and now in the British Museum, are so fragmentary that, in the absence of any record of their discovery in immediate association with vertebrae of the recognized Cetiosaurian type to authenticate them, the correctness of their reference to this genus is open to doubt; and there is the same uncertainty respecting the large bone in the Oxford Museum provisionally assigned to Cetiosaurus, and also with regard to the great Hythe saurian assigned by Prof. Owen to Polyptychodon.

It must be conceded that the limb-bones of these two genera have not yet been certainly identified ; and therefore statements regarding their structure can be of little value.

So far as relates to the absence of a medullary cavity, this Kim- meridge humerus agrees with what has been published oPolypty- chodon and Cetiosaurus ; but it completely difiers fr them both in the compactness of its tissues.

It is also unlike the humeri of the Dinosaurs, Iguanodon and Hyloeosaurus ; and, so far as the material within my reach has enabled me to judge, it is not like that of Megalosaurus ; but the bones in the British Museum considered to be humeri of this saurian are too fragmentary for the comparison with them to be final. The bone with which in its general features it agrees more closely than with any other known to me, is one formerly in the late Dr. Mantell's collection and now in the British Museum. It was regarded by Dr. Mantell as a right humerus (an opinion adopted by