734 Davis — On the Fossil Fish-Remains of the Coal Measures of the British Islands. 



This species is peculiar from its great length in proportion to the diameter. 

 Its curved form distinguishes it from all other species, which have the denticles 

 arranged on the directly opposing lateral surfaces of the spine. 



Formation and Locality. — Bone-bed, Better-bed Coal, Clifton, near Halifax 

 (Lower Coal Measures). 



Ex coll. — James W. Davis. 



Pleuracanthus denticulatus, Davis. 

 (PI. Lxxii., figs. 18-20.) 



Pleuracanthus denticulatus, . Davis, J. W., 1880, " Quart. Journ. Geol. Soc," 



vol. xxxvi., p. 334, pi. xii., fig. 7. 



Pleuracanthus denticulatus, . "Woodward, A. S., 1889, " Cat. Foss. Fishes, 



Brit. Mus." pt. I., p. 9. 



Pleuracanthus denticulatus, . Woodward & Sherborn, 1890, " Cat. Brit. Foss. 



Verteb.," p. 154. 



Spine: base wanting; length 0-055 m. ; distinctly curved ; lateral and anterior 

 face smooth ; circular in section ; the posterior surface is flat, with two rows of 

 denticles separated by a distance equal to one-half the diameter of the spine. 

 The denticles are small, closely set together, broad and strongly attached at the 

 base, contracting suddenly, and forming a carinated apex, pointing towards the 

 base of the spine. 



There are forty-five denticles on each side on the length preserved. A some- 

 what large central cavity extends towards the apex. 



This specimen is from the Bone-bed above the Better-bed coal, and from that 

 locality is unique ; other specimens have been found in the shale above the cannel 

 coal at Tingley, which differ little from the type ; they have similar closely set 

 strong denticles. The sides are somewhat compressed, and towards the base have 

 slight striae. It is possible that if the base of the Bone-bed specimens were pre- 

 served, its surface might be ornamented in the same way. The lower part of the 

 spine is thin, and the internal cavity large ; the walls expanding towards the base. 

 A perfect example would probably be 0'09 m. in length. They are composed of 

 a dense bony substance (fig. 18). 



This species differs from all the others obtained from the West Riding coal 

 field in its arched form, and close, peculiar denticulation. Pleuracanthus arcuatus, 

 Newberry,* afterwards described and figured by the same author as Orthacanthus 



* Proc. Acad. Nat. Sci., Pliiladelpliia. 1856. 



