142 MAEINE EEPTILES OF THE OXFOED CLAY. 



sides they bear, on slight prominences, large rounded facets for the caudal ribs ; the 

 ventral face is very gently convex from side to side, and may or may not be perforated 

 by nutritive foramina. Further back the caudal centra become deeper and narrower, 

 the greater depth being mainly due to the development of a pair of strong longitudinal 

 ventral ridges, the posterior ends of which are obliquely truncated by facets for the 

 chevrons. Between these ridges the surface of the centrum is concave from side to 

 side, as it is also between the ridges and the costal facets. The ends of the centra in 

 this region are more strongly concave than further forwards. In the hinder part of 

 the tail the ventral ridges become very strongly marked, and towards the end of the 

 column they are produced into strong tuberosities which may coexist with chevron- 

 facets, and therefore are not fused chevrons ; these last-mentioned elements extend 

 to the termination of the tail. In the caudal region the neural arches are low with 

 stout pedicles, which unite with the anterior three-fourths of the centrum ; the neural 

 spines are short, stout, and inclined backwards. In the middle of the tail the zyga- 

 pophyses are well developed, but further back they are reduced and at last disappear, 

 and in a few of the terminal caudal vertebrte it is doubtful whether the neural arch 

 was present at all. 



A number of small bones of peculiar form, associated with the caudal vertebrae, seem 

 to be caudal ribs. If this determination be correct, it would appear that the ribs of some 

 of the caudal vertebras united with one another at their outer ends by facets and in some 

 cases even fused ; it might be suggested that these bones were chevrons, but their 

 articulations do not seem to fit tlie chevron-facets. 



The shoulder-girdle (PL VII. figs. 2, 2a; text-fig. 70) in the type specimen is well 

 preserved. The clavicular arch has been figured and described in detail by Professor 

 Seeley *, who states that " The interclavicle was found in situ, resting on the visceral 

 surface in a depression between the anterior margins of the scapulae and not projecting 

 in advance of those bones. It is lanceolate in contour, 2f inches long. If inches wide 

 towards the slightly concave anterior margin, and half as wide at the rounded 

 posterior extremity. It is a little distorted, like the other bones of the shoulder-girdle, 

 has a flat visceral surface and an angular ventral surface, due to the bone being 

 traversed by an elevated median ridge, which dies away anteriorly, and from this ridge the 

 lateral surfaces are inclined. On the left side of the ventral surface its middle part is 

 covered by a thin film of bone, which I suppose may be part of the clavicle. It corre- 

 sponds in texture and thickness with a detached film of bone which rests upon the right 

 scapula. That ossification is triangular, about IJ inch in each measurement, and has 

 nearly straight sides. It is quite separate from the interclavicle and lies towards the 

 external border of the scapula ; there is no surface for its articulation, for all the 



* Proc. Eo\al Soe. vol. 51 (1892) p. 143. 



