PISH OP THE CARBONIFEROUS PERIOD. 13 



Astet'optychius semiornatus (M'Coy). 



Sp, Char. Ray slightly arched, about 3 lines wide, and tapering 

 at the rate of about 1 line in 1 inch ; section much compressed, 

 the sides being flattened, and the thickness about one-third 

 the width j about eight narrow, longitudinal smooth ridges on 

 each side, separated by flat spaces nearly twice the width of 

 the ridges ; all the spaces are marked with two or three obso- 

 lete longitudinal striae, but only the anterior one on each side 

 contains a row of irregularly placed tubercles. 



This is more compressed and arched than the A. ornatus (Ag.), 

 and difi'ers besides in having but one row of tubercles on each 

 side, while that species has a row in nearly every space. 



Not uncommon in the Armagh limestone. 



{Col. Cambridge University, &c.) 



Erismacanthus (M'Coy), n. g. 

 (Etym. epeca-fiaj a prop or stay, and ciKavOa, a spine.) 



Gen. Char. Spine of three divaricating portions, — 1st, a large, 

 compressed, finely striated base which entered the flesh ; 

 2nd, a short, strongly compressed, rapidly tapering spine 

 curved directly backwards, the sides marked with strong, 

 smooth, longitudinal ridges, and having two rows of short 

 downward-curved teeth on the posterior concave margin j 

 3rd, a peculiar prop-like portion extending directly forwards 

 nearly at right angles with the base, gently arched downwards, 

 compressed at the basal half, depressed at the distal half, 

 closely covered with blunt, smooth, oval tubercles, and with 

 some large, irregular spines on the under side ; the portion of 

 the base above the flesh and from which those two portions 

 branch, is irregularly tuber culated. 



The long anterior prop or stay-like branch renders this ich- 

 thyodorulite so unlike any described form, that I should have 

 hesitated to describe it, but for the number of examples which I 

 have recently examined. Something slightly analogous I observe 

 in the articulation of the spines of the recent fish allied to Syno- 

 dontus, in which a shorter but similarly curved and directed prop- 

 like process may be observed, but which is concealed beneath the 

 soft parts and not external as in the fossil. I know but one 

 species of the genus, which 1 have great pleasure in dedicating 

 to Capt. Jones, R.N., M.P. &c., who is in possession of more 

 extensive and exact knowledge of the fossil fishes of the moun- 

 tain limestone than I believe any other observer. It is to his 

 acumen in recognising the true characters of the species, zeal in 

 collecting, and liberality with which both his cabinet and infor- 



