not more than an inch long; they are only slightly arched, with the head a little enlarged and the distal extremity obtusely pointed. Further in advance there are the remains of three or four other ribs, with more or less of the enlarged proximal extremity preserved and lying on the vertebrae apparently near to the point of articulation. One such extremity, the most anterior, is pressed down upon the sixth or seventh vertebra in advance of the sacrum. It lies immediately behind and below the distorted and broken transverse process, to which it is probably attached. Portions of the other heads occupy relatively exactly the same position on the two posterior vertebrae.
The head of each rib is of a triangular form, and is compressed, with the articulating surface simple and almost straight. The shaft at the proximal extremity is rather strongly bent ; it is afterwards slightly and regularly arched, and at first it is narrow and almost cylindrical, afterwards it widens and flattens, and is grooved longitudinally; the distal end is truncated for the attachment of the ventral ribs, of which, according to Meyer, there are three to each vertebral rib. The ventral ribs are not preserved in our specimen, with the exception of one or two. Two or three ribs on a portion of the counter-slab measure 4-3/8 inches in length along the chord. The widened extremity is 1/4 inch broad; the constricted portion above is not more than half that width.
Proterosaurus Huxleyi, n. sp. (P1 XL.)
The small specimen of Proterosaurus, though far from being perfect, is not by any means so much mutilated as the large example of the genus above described. It lies apparently on its belly, with the two anterior limbs spread out, and the principal bones of the left posterior limb lying nearly in their natural order, though dislocated. In front of the trunk the neck-joints are scattered about in contact with the right coracoid ; and a little further in advance towards the left is apparently a fragment of the skull, an arched bone 5/8 of an inch in length. The lumbar vertebrae are not present, and the proximal caudal vertebrae are likewise deficient, the slab being broken away at this point ; but a few of the distal ones can be traced. The ribs are spread out on either side of the spinal column, which strongly marks the central line. The trunk of the body from the pelvic region, or from the point where the slab is broken away, to a point level with the supposed cranial fragment, is about 5 inches in length.
The bones are in a peculiar state. The surface of most of the limb- bones and ribs is well preserved : these bones seem to have been hollow, and are filled up with galena ; but the vertebrae and some of the smaller bones, such as the carpals, are almost entirely composed of that mineral ; and when this is the case, the form of the bones is often much distorted, apparently by the influence of the lead-ore in assuming its usual cubic form.
The vertebrae are not in a good state of preservation ; they are much injured by the deposition of the galena, as above referred to, which has so distorted the form of the bones that it is quite impos-
