358 Messrs. Hancock & Atthey on Reptile- and Fish-Remains 



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

 outer margin of the plate ; a little further back it is almost 

 invariably removed ; and still further back, on the older por- 

 tion 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 Ctenodus we possess. Were 

 we, then, ignorant that the sections 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 disposed to create sjDCcies, 

 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 section. 



Palceoniscus Egertoni^ Agassiz. 



Two large patches of scales, representing the greater portion 

 of the fish, have occuiTcd at Newsham. The scales are in a 

 very good state, and show the characteristic markings of this 

 very j)retty species ; when examined with the microscope, it 

 is perceived that the surface of enamel is regularly covered 

 with extremely minute punctures or dots. The larger patch 

 is one inch and five-eighths long, and upwards of three-eighths 

 of an inch wide. The fins are not displayed; neither are there 

 any traces of head or tail. 



Several other PalcBonisd have been found in our shales, as 

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

 the collection a specimen or two of what we take to be a spe- 

 cies of Eurylejpis, Newberry. Though these are not in a very 

 perfect condition, they are in a much better state of preserva- 

 tion than the specimens of P. Egertoni. In many of them the 

 head is present ; and both the tail and fins are frequently de- 

 terminable. Several of them are probably new ; but at pre- 

 sent we cannot enter more fully on this branch of the subject, 

 and must leave it for some future opportunity. A few words, 

 however, may be said on the dentition of these fishes, particu- 

 larly as it seems to be little understood; indeed it appears 

 that little or no attention has been given to this matter. 



M. Agassiz, in his great work, ' Poissons Fossiles,' states 

 that the teeth of Palceoniscus are " en brosse " (tome ii. pt. 1. 

 p. 42); but the words which immediately precede this expression 



