568 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 8, 
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 vertebre 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 vertebre. 
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 longi- 
tudinally; 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 43 inches in length along the chord. 
The widened extremity is + inch broad; the constricted portion 
above is not more than half that width. 
Prorerosaurus Hvxieyi, n. sp. (PI. XL.) 
The small specimen of Proterosaurus, though far from being per- 
fect, is not by any means so much mutilated as the large example 
of the genus above deseribed. 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 dis- 
located. 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 2 of an inch in length. The lumbar vertebra are not present, 
and the proximal caudal vertebre 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 ina 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 vertebra and some 
of the smaller bones, such as the carpals, are almost entirely com- 
posed 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 vertebree 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 1s quite impos- 
