FISH OF THE CARBONIFEROUS PERIOD. 15 



Platycanthus (M'Coy), n. g. 

 Gen. Char. Ray triangular, very wide, the length of the base 

 nearly equalling the height of the spine, arched backwards, 

 much compressed ; sides flat ; anterior face flat, the thickest 

 part of the ray ; surface pustulated ; two rows of sharp conical 

 teeth on the posterior face. 



In their great compression and pustulated surface the rays of 

 this genus resemble the Oracanths, but they differ from them by 

 their small size, arched form, and distinct posterior rows of teeth, 

 which latter character also distinguishes them from the Byssa- 

 canths of the old red sandstone, as well as the absence of ridges 

 on the surface. I only know the genus in the mountain lime- 

 stone. 



Platycanthus isosceles (M^Coy). 



Sp. Char. Length of the base and hei'i;ht of the spine each about 

 1 inch ; anterior face 1 line wide in the middle and slightly 

 convex ; surface covered with numerous smooth, oval or rounded 

 tubercles subquincuncially arranged, largest towards the an- 

 terior face, about twice their diameter apart ; intervening sur- 

 face marked with minute, longitudinal rough sulci ; posterior 

 teeth conical, smooth at the apex, longitudinally plicated at 

 the base. 



Rare in the carboniferous limestone of Armagh. 

 [Col. Capt. Jones, R.N., M.P.) 



Nemacanthus priscus (M'Coy). 

 Sp. Char. Ray much elongated, slightly arched, compressed to- 

 wards the anterior face, which forms a prominent rounded 

 ridge or keel ; sides with numerous unequal, irregularly placed, 

 oval, blunt tubercles, between which the surface is marked 

 with longitudinal rows of minute impressed puncta, and a few 

 irregular impressed flexuous striae ; base attenuated and finely 

 striated. 



This spine agrees with the Triassic Nemacanths in having the 

 sides flattened and inclined towards the anterior face, on which 

 is a central rounded ridge or keel. The only specimen I have 

 seen is imperfect, measuring 3^ inches in length ; the broken 

 distal extremity is 4 lines in antero-posterior diameter and 2 lines 

 wide. 



From the red limestone of Armagh. 

 (Col. of Capt. Jones.) 



Dipriacanthus (M^Coy), n. g. 



(Etym. 3t9, bisy Trpccov, serra, and ciKavOa, aculeus.) 



Gen. Char. Spine small, arched, tapering, much compressed, 



