340 FOSSILS FROM THE 



and which that of Asterolepis also illustrates, I suspected, 

 but was not prepared to establish, a few months ago, when I 

 published my little work, the " Foot-prints ;" but from spe- 

 cimens since found, it can now, I think, be substantiated. In 

 most of the placoids, the teeth ranged along their jaws or 

 palates, and the shagreen points spread over their skins, seem 

 equally of dermal origin, and can be stripped off with the 

 integuments on which they rest. And so nearly do they ap- 

 proach in character, that there are cases in which they can 

 scarce be distinguished : the teeth may be taken for shagreen 

 points, or the shagreen points for teeth. This is strikingly 

 the case in Cestracion Fhillipi (the Port- Jackson shark). "We 

 find immediately within the more characteristic pavement 

 teeth of the animal, osseous points of an irregularly cruciform 

 shape, that might be mistaken for the osseous points, also 

 irregularly cruciform, that form the shagreen which covers 

 its back and sides ; and the palate of Squatina (the angel 

 fish) bristles as thickly with a shagreen hardly distinguish- 

 able from that which the creature wears outside, as any part 

 of its body. Now, in the base of the head of Z)^p^er^ts [Spec. 13], 

 immediately between its angular patches of palatal teeth, we 

 find exactly the same glossy enamel as that which covers its 

 dermal plates and scales ; the shin within the mouth, if one 

 may so speak, completely corresponds with the skin outside. 

 We find it bearing the same rich gloss, and punctulated by 

 the same microscopic tubes. There occurs what seems to be 

 a similar reproduction of dermal peculiarities within the 

 mouth of the Asterolepis. It was lined with osseous plates, 

 identical in their internal character with those which covered 

 the head externally, and, like them too, was thickly fretted by 

 tubercles, which in the older and larger individuals assumed 

 the normal star-like character, and in both young and old 

 manifested atendency, where they approached the true teeth, to 

 assume tooth-like forms [Spec. 14.] The base of the head in 



