UPPER, OR FLINTY CHALK. ^31- 



Locality. Upper chalk, near Lewes. 



1 10. Part of a dorsal fin. Tab. xxxiv. fig. 8. 



This fragment consists of five parallel rays ; it difiers from those 

 above mentioned, in its surface being marked with obhque finely serrated 

 sutures * ; the interior is hoUow, and fiUed with chalk. 



LocaUty. Upper chalk, near Lewes. 



Two other dorsal fins, apparently belonging to different species of the 

 same tribe of fishes, have very recently been discovered. One of them is 

 from the grey marl ; it is composed of twelve or thirteen rays, the upper 

 ones being distinct, and the lower ones anchylosed ; it is ten inches long, 

 and 1 -5 inch wide at the base : both margins are entire, but it is probable 

 that the uppermost ray may be wanting. 



The other fin is imperfect; the rays are very slender, nearly cylindrical, 

 and quite distinct from each other. 



111. Teeth of fishes allied to the genus Diodon. Tab. xxxii. figs. 18, 

 19, 20, 23, 24, 25, 29. 



These teeth are more or less of a quadrangular shape, having the 

 outer surface convex, and composed of an exceedingly hard enamel, which 

 in the centre is formed into sharp and slightly curved ridges ; these are 

 surrounded by a border of obtuse papillae. The specimens before us 

 exactly resemble the teeth of the Diodon histrix, which has one tooth of 

 this kind affixed to the os hyoides, and another to the palate or roof of the 

 mouth. But the fossil teeth are sometimes found in considerable numbers, 

 and of various sizes, forming a tesselated surface of several square inches ; 

 and so regularly disposed, the smaller palates being adapted to the in- 

 tervals between the larger ones, that no doubt can exist of this having 

 been the mode in which they were placed in the original. Hence, instead 

 of each specimen being a distinct palate, hke the corresponding teeth of 

 the Diodon, they appear to have constituted the covering of the entire 

 roof and base of the mouth f. 



* I am informed by Mr. Konig, that a similar structure is perceptible in the fin figured by 

 Townsend, whicli is now in the British Museum. 



-f- These teeth are termed by Mr. Miller, dentes tritores : " they differ from the molares, in 



