Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/507

 Owen), and it is the bone on which Mantell founded his genus Pelorosaurus. But the agreement is not complete ; for, besides the much greater size of the Pelorosaurian humerus, which cannot be altogether explained by assuming the bones to have belonged to individuals of different ages (because the smoothness and compact texture of the Kimmeridge bone, and the absence of the large and numerous vascular foramina so conspicuous near the articidar end in young and growing crocodiles, show it to have belonged to an adult animal), there are variations of details, amongst which I may cite the very different form of the transverse sections of the shafts and the presence of a medullary cavity in Pelorosaurus.

We have, then, in this humerus evidence of the existence during the Kimmeridge period of an immense saurian fitted for terrestrial progression, with strong crocodilian affinities, but differing from any yet completely known to us ; of such a gigantic saurian we had already traces in a great ungual phalanx from the Kimmeridge clay of Ely and a fibula from near Weymouth, both in the British Museum, and in a cast of a large tibia also in the same collection, the original of which I think I have seen in the Woodwardian Museum labelled " Macrochelys^'*.

Measurements.

inches. Length 31 Girth of shaft at a 13

Proximal end: — Length of terminal surface along the curve 11 Maximum width of terminal surface 4.5 Width near anterior angle 1.5 " at posterior angle 1 Girth 21 Direct line between anterior and posterior angles of terminal surface 8

Distal end : — Girth 24 Transverse diameter of terminal surface 9 Width (from upper to under surface) of posterior condyle 5 " of anterior condyle 3.5 " at intercondyloid notch 3

EXPLANATION OF PLATE XVI.

Left Saurian humerus from Kimmeridge Bay. In the Collection of J. C. Mansel, Esq.

[The fractions annexed to the figures indicate the extent of the reduction from the natural size.]

Fig. 1. Under (or anterior) surface: a, anterior (or outer) border; b, proximal end ; c, distal end.

2. Upper (or posterior) surface : a, posterior (or inner) border ; b, proximal end; c, distal end.

3. Proximal terminal surface.

4. Distal terminal surface : a, anterior ; b, posterior end.

5. Transverse section of shaft, showing the absence of a medullary cavity : a, anterior, b, posterior surface.

[* Mr. Seeley informs me that the name of" Gigantosaurus megalonyx" has now been attached to this specimen. — W. S. D.]