Coal-measures of Northumberland. 219 



scars of denticles that had become detached ; but the most 

 careful examination of the counterpart of two of the largest of 

 them failed to reveal the slightest trace of tubercular or denti- 

 cular structure. 



Comments. The base of the spine is unfortunately wanting, 

 so that it is impossible to say at what angle it was inserted in 

 the body of the fish. From its great length and slenderness 

 it may be conjectured that it was set at a very low angle, or 

 that it was supported for the greater part of its length by a 

 strong cartilaginous structure ; it seems weak as a defensive 

 weapon, compared with what was probably the large size of 

 the fish. 



Relations and Differences. In discussing its relations to 

 genera previously described, it will be enough to notice at 

 length two only, viz. Leptacanthus and Ort/iacanthus, both 

 established by Agassiz. Agassiz's Leptacanthus was founded 

 upon Jurassic specimens. L. longissimus from Caen was 

 doubtfully put by him in the genus. He says " Je le signale 

 plutot a l'attention des paleontologistes que je n'espere en 

 donner une description satisfaisante." He is doubtful as to 

 the serration and as to the ornament. Until the spine is 

 better known it would be unwise to say much about it. If 

 Agassiz's account of it is correct, Mr. Taylor's specimen differs 

 from it by important characters. L. longissimus is finely 

 serrated on the posterior margin, compressed, and shows in 

 cross section a concave posterior area. Two spines from 

 Carboniferous rocks have been referred to Leptacanthus by 

 M'Coy (Brit. Pal. Fossils, p. 633) ; both, however, differ by 

 important characters from Mr. Taylor's specimen. 



Curved spines have been referred to Orthacanthus by J. S. 

 Newberry (Pal. Ohio, vol. i. p. 332). He believes the 

 straightening is due to pressure. Orthacanthus appears to be 

 rare in the British Coal-measures, but is usually, when re- 

 ferred to, described as straight. Whether curved or straight, 

 the generic distinctness of the specimen I am describing will 

 not, I think, be affected. The structure of the posterior area, 

 the absence (?) or, if it may be said to exist, the peculiar 

 nature of the denticulation, and the general facies of the 

 spine separate it from that genus. The same assemblage of 

 characters separates it also from Phricacanthus, a spine de- 

 scribed by Mr. J. W. Davis, F.G.S. (Q. J. G. S., May 

 1879). 



I have no data by which to connect it with teeth or other 

 remains of diagnostic value. The specimen appears to be 

 unique. Until discovery throws light upon its true affinities 

 it must remain as the type of a new genus, which I propose 



