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-of them, regularly disposed, constituted the platform of the palate of some 

 unknown fish. 



The palate of another species of unknown fish appears to have been 

 formed by the regular arrangement of quadrangular bodies, a beautiful 

 specimen of one of which is figured Plate XIX. Fig. 18. The hard part 

 of these bodies, corresponding to the enamel of teeth, is disposed, on the 

 middle part of the upper surface, in sharp and slightly-curved ridges, 

 alternating with corresponding depressions. These are surrounded by a 

 border, formed of obtuse papillae and rugae, disposed in a very confused 

 and irregular manner. In some specimens, this border is not present. 

 These palates are chiefly found among the chalk of Kent and Surry. 

 The most interesting fossil of this description, which I possess, is one 

 which is imbedded in the centre of a nodule of flint. 



The fossil, Plate XVIII. Fig. 12, is one of the component parts of the 

 roof of the mouth of some other unknown fish. It resembles the preceding 

 fossil in the disposition of its ridges, &c. but differs from it in having a 

 much greater convexity, being full as high as it is long. It is found, 

 though much more rarely than the former, in masses of chalk, and most 

 frequently in the neighbourhood of Devizes, in Wiltshire. 



Several of this, and of the two preceding species of fossil palates, 

 were exposed to the action of dilute muriatic acid ; when the existence 

 of their membranous laminae was evinced by numerous delicate flocculi 

 becoming partly detached from the surface. In the leech-like palate, 

 the phenomena which occurred were very interesting. After the fossil 

 had been exposed about twelve hours to the action of the acid, its dark 

 surface gradually disappeared, and was succeeded by one of a silvery 

 grey colour, having somewhat of a pearl-like lustre. On this being exa- 

 mined with a lens, it was found to be an exceedingly fine membrane, 

 which, on being touched with the finger, was immediately removed, 

 and with it the rugae with which the surface had been originally marked. 

 On being suffered to dry, the surface became of a dead white, and 

 marked the fingers, the rugae being nearly effaced. 



