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



Pleuracanthus Thomsoni, sp. nov. 



(PI. LXXIII., fig. 17.) 



Spine : distal extremity absent ; length preserved 0-8 m ; greatest diameter 

 0-06 m. ; section circular, with round internal cavity. If perfect the spine would 

 probably be 0'9 m. in length. The denticulated surface which is preserved occupies 

 0-18 m., and consists of a double row of eleven denticles separated by a distance 

 of rather more than 0-02 m. ; the intervening space is occupied by a ridge. The 

 denticles are broad and obtuse, with a broad lateral depression between each. 

 The spine is slightly curved. 



This species approaches most nearly to P. rohistus, Davis, in general ap- 

 pearance. It differs in being thinner in proportion to its length. The denticulated 

 surface is shorter, and the two rows are closer together. In P. robustiis, the den- 

 ticles extend over half the length of the spine ; in this one they cover little more 

 than one-fourth. The denticles themselves are short and rounded, whilst in the 

 former they are closely implanted, recurved, pointed, and extend from the surface 

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



Formation and Locality. — Above the soft coal in the Red Sandstones at Quarter 

 Hamilton, Kilmarnock. 



Ex coll. — James Thomson, Glasgow. 



Pleuracanthus obtusus, nom. nov. 



(PI. LXXIII., fig. 18.) 



Phricacanthus biserialis, . . Davis, J. "W., 1879, " Quart. Journ. Geol. Soc," 



vol. XXXV., p. 186, pi. X., figs. 16, 17. 



Spine: length 0-105 m.; greatest diameter 0.007 m. The spine is gently 

 arched backwards, the exposed part covered with minute longitudinal striations. 

 In section the spine is circular : from the apex extending 0'05 m. along the pos- 

 terior surface, there is a right and left row of seven widely separated protuberances 

 or denticles. In the lower part there is a distance of 0-007 m. between the apex 

 of two consecutive denticles ; they are broad longitudinally, laterally compressed, 

 and rapidly converge to a rounded obtuse apex. The denticles are alternate, the 

 projection on one side being opposite to the depression on the other ; an internal 



