Osteology of Caturus and Osteoracliis. 293 



by the British Museum, and the numbers in brackets always 

 refer to the Register of the Department of Geology. 



Cranium. 



The chondrocranium exhibits extensive ossifications, but 

 was not sufficiently resistant to withstand complete collapse in 

 the soft clay. The basioccipital is deeply excavated on its 

 posterior face by a conical fossa for the notochord, and the 

 inferior aspect of the bone (no. P. 6901) is marked by a 

 longitudinal groove, though this is not covered by tlie para- 

 sphenoid and there is apparently no basicranial canal. There 

 are robust ossifications in the postfrontal and prefrontal 

 (lateral ethmoidal) regions, but cartilage must have persisted 

 in the mesethmoid, which can only have been small. In the 

 lateral wall of the cranium, immediately in front of the post- 

 frontal, there appears a very large ossification, longer than 

 deep, which is probably to be identified with the alisphenoid 

 (no. P. 6906) ; a smaller, nearly quadrate ossification adjoins 

 this behind, and seems to correspond with the pro-otic of 

 Amia (seen in same specimen) ; and a third bone, occurring 

 still further back, quite at the angle of the occiput (seen in 

 no. P. 6901), agrees well with the opisthotic of the same 

 genus. The latter element is shown to be pierced by a large 

 oval foramen, evidently for the exit of the vagus nerve. 

 A great parasphenoid sheaths most of the base of the 

 cranium, forked posteriorly and not quite reaching the 

 occiput, comparatively broad in advance of the basiptery- 

 goid processes, and provided in this region with an elongated 

 lenticular patch of very minute teeth. Each basiptery- 

 goid process was evidently much elongated, reaching the 

 postfrontal above. The parasphenoid extends as far for- 

 wards as the prefrontal region, there expanding a little and 

 meeting the pair of large vomers. These two bones meet 

 throughout their length, but are not fused in the median 

 line, and each is about three times as long as broad, bearing 

 a few teeth only at its anterior end. The bases of about four 

 of these vomerine teeth are shown in no. P. 6901. The 

 membrane-bones of the cranial roof form a continuous flat- 

 tened shield, and in large individuals its principal elements 

 sometimes appear to be fused together. The occipital border 

 is straight (PI. VIII. fig. 1, occ), formed, as usual, by the 

 parietals and squamosals. The parietals {pa.) are shown, in 

 nos. 29049, P. 6908 c, to be relatively small, with the wavy 

 suture between them not quite mesially placed, and each sends 

 forwards at its outer margin a long pointed process inter- 



