an inch thick, arid the proximal extremity is nearly double that thickness, the increase being due in part to a ridge, apparently at the outer or upper surface.
The tibia and fibula are 1-1/10 inch long, so that they are a little more than 1/8 of an inch shorter than the femur. They are nearly straight ; the fibula is slender, and does not seem to have been much enlarged at the extremities, which are, however, not perfect. The tibia is considerably stouter, but not by any means so thick as the femur. The distal end is gradually thickened a little, but the proximal extremity is considerably and rather suddenly enlarged. In this, as in all the other bones, the articular extremities, having been formed of cartilage, are wanting, the ends being truncated. It is therefore quite impossible to describe in detail the characters of the joints.
Fragments, apparently of the right tibia and fibula, and three or four of the phalanges, are scattered about in the vicinity of the bones of the left leg ; but no other traces of the right limb are to be found.
The only portion of the pelvic girdle present is the extremity of a flat bone. This fragment is 3/10 of an inch long, and 2/10 of an inch wide ; it slightly widens towards the anterior extremity, which is truncated. This is probably a portion of the ilium.
From the above description it seems evident enough that this small reptile is a true Proterosaurus, and that it is specifically distinct from P. Speneri. The long articulating limbs and extensively produced tail are common to both species. In both, too, the neck has been of considerable length, and the number of cervical vertebrae (seven) is apparently the same in both. And the number of the dorsal vertebrae would likewise appear to agree in both species, and in each there are numerous ventral ribs. The same harmony is found in the number and character of the hand-bones. Unfortunately no comparison can be instituted respecting the skulls and the individual features of the vertebrae, as these parts in the new species are too imperfectly preserved ; enough, however, seems to be known to warrant the assertion that the two are generically coordinate.
It appears equally clear that the small individual is specifically distinct. The diminutive size alone suggests this, especially as there are no appearances of immaturity ; and the form of the ribs would seem to prove its specific distinctness. In P. Huxleyi we have seen that they are flattened towards the proximal extremity, while in P. Speneri they are rounded at this part; and in the former they are not widened and grooved to any thing like the same degree at the distal extremity.
The limbs, too, are proportionately different. In P. Speneri the fore limb is 4-7/8 inches long, as figured in von Meyer's work, tab. ix. The hind limb is 7-5/8 inches in length ; consequently the former is 1/3 shorter than the latter. In P. Huxleyi the fore limb is 1-7/10 inch in length, the hind limb 2-3/8 inches long ; the former in this species therefore considerably more than 2/3 the length of the latter.
In the new species, then, the limbs vary more in length than they
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