62 REPORT — 1841. 



the flattened surface is polished, but marked with minute shallow wrinkles ; 

 one of the ridged surfaces, which stood at right angles to the preceding, was 

 traversed by eleven well-marked linear ridges of unequal length, separated 

 by smooth interspaces of about three times the breadth of the ridges ; the 

 third surface, which formed an acute angle with the smooth outer surface, 

 was traversed by twelve ridges. These ridges, on the inner surface of the 

 tooth, slightly inclined towards the rounded angle, dividing the surfaces ; they 

 terminate abruptly ; some cease half way from the apex of the crown ; about 

 ten are continued to within half an inch of the apex, which is smooth ; the 

 two ridges, which divide the flat or smooth side from the ridged surfaces of 

 the tooth, are alone continued to the subacute apex of the tooth. 



The teeth of the Pliosaur present varieties of form as well as of size ; the 

 rounding off" of the angle between the ridged surfaces has been already alluded 

 to ; the smooth outer surface is sometimes so convex, that the transverse 

 section of the tooth is more elliptical than triangular. All the teeth of the 

 Pliosaur are slightly bent inwards and backwards ; but the smaller posterior 

 teeth are most recurved, and have the sharpest apex ; and in the crown of 

 these teeth the ordinary rounded or elliptical form of the cone is most 

 nearly attained ; but the distinction of the smooth external surface, and the 

 ridged internal surfaces of the crown of the tooth are retained, and would 

 suffice to characterize any of these teeth if found detached. 



The teeth consist of a central body of compact dentine, with a coronal 

 investment of enamel, and a general covering of cement. The dentine is 

 permeated by fine calcigerous tubes, without admixture of medullary canals. 

 The arrangement, division, secondary undulations, and branches of the cal- 

 cigerous tubes closely correspond with those of the teeth of the Plesiosaur. 

 The germs of the successional teeth in the Pliosaur were developed at the 

 inner side of the basis of the old teeth, but did not penetrate these teeth ; the 

 apices of the new teeth make their appearance through foramina situated at 

 the inner side, and generally at the interspaces of the sockets of the old teeth. 

 Here, therefore, as perhaps also in the Pterodactyle, the growing teeth may 

 be included in closed recesses of the osseous substance of the jaw, and 

 emerge through tracts distinct fi'om the sockets of their predecessors, which 

 is an exceptional condition of the reproduction of the teeth in reptiles. 



Of the Vertebral Column. — A long neck has been considered to be so 

 peculiarly the distinction of the Plesiosaur, that a species which has this 

 part of the spine shortened and reduced by the flattening of the vertebrae to 

 Ichthyosaurian proportions, may be reasonably regarded as at least subgene- 

 rically distinct, especially when the enormous and massive head, to which the 

 abbreviated neck bears a subordinate relationship, is armed with teeth which 

 have just been shown to be as remarkable for their thickness and strength as 

 those of the Plesiosaurus are for their slender and sharp-pointed proportions. 



Perhaps there is no example, save the genus Pliosaurus, in the whole class 

 of reptiles, living or extinct, which has any of the vertebrae presenting such 

 proportions as those of the followijig specimen in Dr.Buckland's collection from 

 the Kimmeridge clay of Foxcombe Hill, near Oxford. The breadth of the 

 body of this vertebra is six inches ; its depth, or vertical diameter, five inches ; 

 while in length, or the diameter corresponding with the axis of the body, 

 it measures only an inch and a half. But cervical vertebrae of similar pro- 

 portions have been discovered in the Kimmeridge clay near Weymouth, and 

 were described by Mr. Conybeare in the ' Geological Transactions.' The 

 Market-Raisin specimen in the Oxford Museum proves that those peculiarly 

 compressed vertebrae are associated with the well-defined teeth characteristic 

 of the Oxford and Kimmeridge clays, and with jaws of great size, which could 



