do in the old ones, the hind limb being considerably longer in the former, in proportion to the fore limb, than is the case in P. Speneri.
The difference likewise is strongly marked in the proportions of the humerus. On referring to von Meyer's tab. ix., above quoted, the constricted part of the shaft of the humerus therein figured measures 3/8 inch wide, while the distal extremity is 9/8 inch across : thus it appears that the latter part is three times wider than the former. In P. Huxleyi the narrow part of the humerus is 1/8 inch thick, and the distal extremity is 2/8 inch wide : so here the disparity is only as two to one, but in P. Speneri it is as three to one. It must be stated, too, that in the old species the proximal end of the humerus is nearly as wide as the distal, while in the new species it is only slightly enlarged.
EXPLANATION OF PLATES XXXIX. & XL.
Plate XXXIX.
Slab of Marl-slate from Midderidge, containing the vertebral column &c. of Proterosaurus Speneri, von Meyer.
Plate XL.
Slab of Marl-slate from Midderidge, containing the skeleton of Proterosaurus Huxleyi, sp. nov., Hancock and Howse.
