I. — Pleuracanthidce. 731 



surface with the sides of the spine are armed with a series of denticles. The den- 

 ticles extend from the apex a distance of 0'04 m. They are large, strongly implanted, 

 closely-set, recurved, and sharply pointed ; about twenty on each side. The upper 

 surface of the denticles, i. e. the one having the greatest curvature, is produced so 

 as to form a miniature carina or keel, smooth and sharp (PI. lxxii., figs. 10, 11). 



Since this species was described in 1880, specimens have been found in other 

 localities. One of these, discovered by Mr. John Ward, in the Knowles Ironstone 

 Shale, at Fen ton, is of peculiar interest (fig. 12). The dorsal or inferior surface is 

 exposed ; the spine is complete, though somewhat fractured in the median part. It 

 is smaller than the Tingley specimens, being 0'086 m. in length. The attenuation 

 of the basal part of the spine, which was implanted in the integument of the fish, 

 is well shown. The walls are comparatively thin and hollow ; they extend to 

 the basal extremity only on the anterior surface ; the internal cavity instead of 

 being terminal is open a distance of 0'012 m. along the inferior surface, the walls 

 gradually enfolding it, as shown in the figure. The number of denticles is the same 

 as in the Tingley specimen. 



This species has also been found in the Lowmain coal seam at Newsham, 

 and a specimen is figured from Mr. Atthey's collection at the Museum at Newcastle. 

 It is complete ; 0-087 m. in length. The lateral surface is exposed, with one row 

 of denticles, extending a distance of 0*03 m. from the point ; they are fourteen 

 or fifteen in number, and of a similar character to those already described 

 (PI. LXXII., fig. 13). 



Spines in all respects similar to the latter are found in the cannel coal at 

 Tingley, but of much smaller size. They appear to have belonged to fishes which 

 were not mature (fig. 14). 



Spines belonging to the fossil fish named by Dr. Fritsch Orthacanthus pinguis, 

 Fr.,* bear a close relationship to this species ; they are larger in size, but the robust 

 form and the arrangement, position, and number of the denticles resemble the 

 spines of P. robustus, Davis. 



Formation and Locality. — Middle Coal Measures, Cannel Coal, Tingley, 

 Yorkshire ; Deepmine and Knowles Ironstone Shale, Fenton and Longton, 

 Staffordshire; Lowmain Coal, Newsham, Northumberland; Carluke. 



Ex coll. — James W. Davis, Halifax ; J. Ward, Longton ; Museum of Natural 

 History Society of Northumberland and Durham, Newcastle-on-Tyne ; British 

 Museum (Nat. Hist.). 



* Fauna der Gaskohle, vol. ii., pt. iv., p. 109, pi. lxxstii., figs. 3, 4, 6. 



