HYPSODON ETC. FROM BRITISH CRETACEOUS STRATA. 519 



The outline of the entire skull has been introduced in the annexed 

 woodcut, to render the relative positions of the parts more intelli- 

 gible. The relation of the bones of the ethmoidal region to the maxilla 

 and praemaxilla is quite certain ; for, although now separated, the 

 broken surfaces show precisely how they fit together. The direction 

 of the outline-base of the skull is determined chiefly by the direction 

 of the under surface of the vomer. In placing the brain-case in the 

 position it occupies, regard has been paid to Prof. Cope's figures of 

 Portheus, as well as to the form of the component bones of the 

 specimen ; but its relation to the other parts must only be 

 taken as approximately correct. The outline of the upper and 

 back parts is, of course, purely conjectural. The lower jaw has 

 been placed low down, out of position, so as not to interfere with the 

 maxilla. 



The skull has been slightly crushed, in a lateral direction, during 

 the process of fossilization ; it is quite certain, however, that it was 

 naturally of a very compressed form. 



Vertebras. — The six vertebrae belonging to this specimen agree, 

 in their general characters, with those which have been referred to 

 the American species ; but, at the same time, they present certain 

 peculiarities. The length of each vertebra is about four fifths of 

 its width -, the terminal faces are deeply concave, and communicate 

 by a small foramen in the centre, as shown in figure 12. One very 

 obvious feature of these vertebrae is the flattening of their lower 

 surfaces ; but, as there are slight ridges towards the terminal faces, 

 this is not so clearly seen in figure 11 as in the specimens. Pro- 

 bably this flattening would not be found in the hinder dorsal verte- 

 brae. The basal portions of the neural arches are left attached to 

 the centra ; and are imbedded in deep pits, one upon each side of 

 the middle line. They do not appear to have been ankylosed to 

 the centra; for the division between the two is clearly seen. The 

 neural canal is small, the part preserved not measuring more than 

 the fourth of an inch in width. Low down upon the sides of the 

 vertebrae, the enlarged heads of the ribs are seen to be attached to 

 the centra, in the same way as the neural arches — that is, by 

 being sunk in deep pits, but not ankylosed. A large and deep de- 

 pression, reaching almost to the centre of the vertebra (fig. 12, Id), 

 is seen upon each side between the neural arch and the rib (fig. 10). 

 This depression is largest in the hindmost of these vertebrae, and 

 smallest in the anterior one. The three vertebrae which appear to 

 have been furthest from the head have a second much smaller de- 

 pression upon each side, placed below the larger one ; and this also is 

 largest in the hindmost vertebra. Judging from the American 

 species, this loss of the lateral depressions in the front vertebrae 

 of this series shows them to belong to the anterior dorsal region ; 

 and probably few intervened between them and the skull. 



Several other pieces of bone were obtained, but they are too 

 fragmentary for determination. Two or three of them may, 

 perhaps, be parts of the clavicles, and another possibly a portion of 



Q. J. G. S. No. 131. 2 m 



