J. W. Davis — Carboniferous Fish-remains, 151 



difficulty with which they are developed from the matrix, they are 

 often fragmentary. An example exhibiting the series of three teeth 

 covering a ramus of the jaw has not yet been discovered. The large 

 posterior teeth are most commonly met with. They are much smaller 

 in size than those of the same species from the Mountain Limestone 

 of Armagh, generally about 0*5 inch in length and 0-3 in breadth. 

 They possess the characteristic convolution of the genus. The 

 enamelled surface of the crown is exquisitely and perfectly pre- 

 served, and in most instances does not exhibit much trace of being 

 worn by attrition, from which it may perhaps be reasonably inferred 

 that they are the teeth of a young individual. 



Genus Psephodus, Agass, MS. 

 Davis, Trans. Eoy. Dub. Soc. n.s. vol. i. p. 438 (1883). 



Psephodus magnus, Ag. 

 Trans, of the Boyal Dublin Society, ser. ii. vol. i. p. 439, pi. 1y. fig. 1-14. 



Several examples of this species have been found. They do not 

 materially differ from the specimens described from the Carboniferous 

 Limestone of Armagh. The largest tooth, probably occupying a 

 median position on the jaw, is 0-85 inch in greatest diameter, more 

 or less pentagonal in outline, the upper surface highly convex, and 

 the under one correspondingly concave. 



A second specimen consists of two teeth joined together similarly 

 to those represented in the memoir named above, pi. lv. fig. 4, the 

 two upper and larger teeth ; the Derbyshire ones are about two- 

 thirds the size of those from Armagh. 



Teeth occur which differ from the types in some particulars. They 

 are almost circular in form, and equally convex from all sides; their 

 diameter across the crown is slightly less than half an inch. They 

 may represent a different species of this genus of fossil fishes, but 

 until a larger number of specimens have been found affording more 

 complete evidence of its peculiar characters, it appears advisable to 

 retain them under the above title as a variety of the old type. 



A number of small helodont teeth are scattered over some of the 

 pieces of limestone. They are small and elongated, smooth and even 

 on the surface of the crown, without median or other prominence. 

 They were probably connected with this or the following species of 

 Psephodus. 



Psephodus simplex, Davis, sp. nov. (Figs. 1, 2, p. 150). 



Teeth trapezoidal in outline, longest diameter 08 inch. Two 

 longest sides forming an acute angle at the apex. The two shorter 

 ones, half the length of the longer, inclosing an obtuse angle. The 

 surface of the crown is convex (Fig. 1), its enamelled surface covered 

 with small punctures. The margins of the tooth are thick. The 

 under surface (Fig. 2) forms a channel extending parallel with the 

 long axis of the tooth, which like the under side of Psephodus magnus, 

 Ag., was attached to one of the cartilaginous jaws of the fish. 



The teeth comprised in this species, of which several specimens have 

 been found, are almost identical in shape. They differ from those 



