260 



parison with a tongue of this kind, found in Mr. Charlton's collection, 

 from the Pastnaca marina, he found their agreement very exact *. 



lam happy in being able to place before you two illustrative speci- 

 mens of this kind. Plate XIX. Fig. 16, is a fossil from the Isle of She- 

 pey, which appears to have belonged to some fish of the genus Raia, 

 being very closely accordant with the recent bony tongue of the fish of 

 this genus, figured, in outline, Plate XIX. Fig. 13. I have another recent 

 specimen of this kind, the jointed bone of which is longer, and exactly 

 agrees with that figured, by Sir Hans Sloane, as the tongue of the Raia 

 pastinaca. 



Another fossil specimen of this kind, in my possession, is considerably 

 larger than the one which I have here figured : and in my friend, Mr. 

 Crow's collection, of Faversham, is one which is six inches in length, 

 and three inches and a quarter in breadth. 



The structure of this body, as is most evident in the analogous re- 

 cent specimen, is singular and interesting. It is formed of two hori- 

 zontally-disposed laminse : the upper of which is of a very close and dense 

 structure, and forms the masticating surface; the other is of a more cel- 

 lular texture. Both these substances are transversely divided into six 

 plates, which are united to each other by very fine and close sutures, 

 and have a row of interstitial substances, of a hexagonal form, placed 

 between their lateral terminations. This body, as appears in the recent 

 specimen, was attached to the surrounding bones : the masticating sur- 

 face is placed upwards in the fossil, as well as in the recent specimen. 



Plate XIX. Fig. 17, is another fossil from Shepey, the general struc- 

 ture of which agrees with the preceding, excepting that, in this body, 

 there appears to have been two rows of hexagonal bodies. As, in the 

 preceding figure, the masticating surface was shown ; so here the other 

 surface, the bony base, is shown ; and this chiefly for the purpose of 

 showing the perpendicular fibres, which, giving to this surface a brush- 



s 



'* Phil. Trans. Vol. xiX. N'o. 232. 



