AND CLASSIFICATION OF THE FOSSIL REPTILIA. 
273 
already described. Anteriorly they are 3 inillims. long, posteriorly are a little 
shorter, are cylindrical, terminate in conical points, and haye slightly expanded bases, 
which are in close union with the jaw. The interspaces between them are about a 
third the diameter of the teeth. They contain sub-cylindrical cavities. The summits, 
or croAvns, of the lower jaw fit into the interspaces between the conical summits of 
the crowns of the maxillary region, and their form is not defined. A The pre-raaxillary 
bones are imperfectly preserved. They were short, as in other specimens, presumably 
divided the nares, were divided medially, and each contained three teeth, which were 
rather longer than those in the maxillary bone, and extend in front of the corre¬ 
sponding teeth of the lower jaw. The shortness of the pre-maxillaries gives a trun¬ 
cated appearance to the snout, since tlieir teeth extend transversely. 
The lower jaw is in natural articulation with the skull. The rami are loosely 
connected, 4T centims. long, and diverge backward, so that the transverse measure¬ 
ment at the quadrate region is equal to the length of a ramus. Each ramus is 
slightly curved, consequent on a slight convergence inward, to make the rounded 
narrow symphysial union ; there is a slight inflection in the articular region, and a 
slight bulging outward below the malar region. 
The lower jaw is comparatively stout, being half a centimetre thick, and it has a 
convex appearance on the external sui'face, and a flattened appearance on the internal 
surface. It is deepest (1 centim.) below the hinder end of the maxillary, whei’e the 
dentary terminates in a slight coronoid elevation, in the middle of the length of the 
jaw, which divides it into an anterior slightly concave tooth-bearing border, and a 
posterior slightly convex area. From below this point the jaw decreases in depth, 
both anteriorly and posteriorly, to less than half its depth in the middle. 
The jaw has lost some of the external bone substance, but appears to include 
five bones. First, on the external surface is the dentary, which forms the whole of 
the anterior tooth-bearing half. Posterior to this there is a long superior bone, 
extending back almost to the articulation, which I regard as the coronoid. It is 
divided by a longitudinal suture from an inferior bone, which extends much farther 
forward than the coronoid, and forms the sharp inferior ridge on the base of the 
hinder part of the jaw, which 1 regard as the angular. On the inner side of the jaw 
two other bones are seen. First, the articular, which is inflected inward to form a 
process like that seen in Birds and some of the lower Mammals. This bone extends 
forward so as to cover the hinder half of the jaw, barely reaching its base, for the 
angular is seen below it; and at its superior termination in front a small bone is seen 
above it, which I regard as the internal extension of the coronoid. The whole depth 
of the dentary appears to be covered internally by another bone, which I regard as the 
opercular. It meets the articular by an oblique suture, which extends downward and 
backward ; and at its inferior termination there is a conspicuous ovate vascular foramen. 
There is a better preserved example of a dentary bone of a new species of Proco¬ 
lophon in the British Museum, B. 514, from Kl. Vogelstruisfontein, in the district of 
2 N 
MDCCCLXXXIX.—B. 
