350 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
by St. John and Worthen, Ctenacanthus burlingtonensts and C. keokuk, should also 
be removed to this genus. 
This species differs from A. tenuistriatus, Davis, in having fewer and broader 
longitudinal ridges, and in the surface of the ridges being more boldly crenulated.. 
Formation and locality : Mountain Limestone, Armagh. 
Ex coll, Earl of Enniskillen. 
Acondylacanthus tenuistriatus, Davis. 
(IE, DW 14% 8) 
Spine, imperfect at both ends, five inches in length, °45 inch wide at basal end, 
from which it gradually diminishes to 3 inch at the opposite one. Transverse 
section sub-triangular, sides much compressed and slightly rounded, anteriorly 
forming an acute angle, latero-posterior angles sharp, base slightly concave, internal 
pulp cavity sublenticular in section, probably terminal at the base, without open 
basal cavity. The spine is gently and uniformly arched posteriorly. The sides 
are covered with about twenty smooth, enameled ridges occasionally slightly beaded 
by exerescences, separated by equidistant intermediate sulci. ‘The anterior margin 
is trenchant, formed of an enameled keel, in some parts of its length presenting a 
slightly serrated appearance. Latero-posterior angles rounded and prominent, 
armed with a double row of small recurved denticles broadly implanted, acutely 
pointed, separated by about twice their own diameter near the distal extremity, 
closer towards the base, posterior surface channeled. Base not preserved. 
It isaremarkable feature in the specimens composing the genus Acondylacanthus 
that the basal extremity has not been preserved. There is in every instance where 
the spines have been described, both American and British, the laconic intimation 
that the base is unknown. 
As already observed this species differs from A. distans in the tenuity of its 
longitudinal ridges and the much finer tuberculation of their surface. It is also a 
longer spine in proportion to its breadth, and more curved, than Acondylacantius 
distans. 
Formation and locality: Mountain Limestone, Armagh. 
Ex coll. Earl of Enniskillen. 
Acondylacanthus junceus, M‘Coy. 
(ERSXGIVAlsticamor) 
Leptacanthus junceus—F. M‘Coy, 1848. “ Apn.and Mag. Nat. Hist.,” 2nd ser., Vol. II.,p.122. 
53 3 J. Morris, 1854. ‘Catal. Brit. Foss.,” p. 332. 
» 9% F. J. Pictet, 1854. ‘Traité de Paléont.,” Vol. II., p. 288. 
55 F. Moy, 1855. ‘Brit. Paleoz. Foss.,” p. 633, pl. 3 G, fig. 13. 
53 5 Morris and Roberts, 1862. ‘‘ Quart. Journ. Geol. Soc.,” Vol. X VIII, p. 101. 
y % prmsirens ung) 1876. ‘Catal. West. Scot. Foss.,” p. 62. 
and Robertson, } 
