96 MESSK3, HANCOCX AND ATTHEY ON 



away. It is, however, generally persistent towards the outer 

 margin of the plate ; a little farther back it is almost invariably 

 removed ; and still further back, on the older portion of the plate, 

 the peripheral wall of hard matter is scarcely ever found, having 

 undoubtedly been worn down by the action of the jaws. It is, 

 therefore, clear enough that, in accordance with the line of the 

 section, we might have the margins of the tooth-like processes 

 rough, without any distinct peripheral wall, as in the figure of 

 the so-called teeth of Saganodus ; or there might be such a wall, 

 without any external enamel ; or, again, both the enamel and 

 peripheral wall might be present : and such a series of sections 

 of Ctcmodus we possess. Were we, then, ignorant that the sec- 

 tions were made from different parts of the same object, we 

 might readily be led to erect three distinct genera on the palatal 

 plate of a single species of Ctenodus. And again, were we dis- 

 posed to create species, various degrees in the obliquity of the 

 section would afford excellent opportunities for so doing, as the 

 tooth-like processes would vary in length and form in each sec- 

 tion. 



Pal^oniscus Egeetoni, Agassiz. 



Two large patches of scales, representing the greater portion 

 of the fish have occurred at Newsham. The scales are in a very 

 good state, and show the characteristic markings of this very 

 pretty species ; when examined with the microscope, it is per- 

 ceived that the surface of enamel is regularly covered with ex- 

 tremely minute punctures or dots. The larger patch is If inches 

 long, and upwards of fths of an inch wide. The fins are not 

 displayed ; neither are there any traces of head or tail. 



Several other PalcBonisci have been found in our shales, as 

 well as one or two species of AmhlyjJterus. There is also in the 

 collection a specimen or two of what we take to be a species of 

 Eurylepis, Newberry. Though these are not in a very perfect 

 condition, they are in a much better state of preservation than 

 the specimens of P. Egertoni. In many of them the head is 



