On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 359 
Genus. —-Lispacanthus, Davis. 
Spine, medium size, ovate in section, laterally compressed, gradually tapering 
to a point. Surface entirely smooth. Pulp cavity internal. Base wide, open 
terminally, walls thin, divided from exposed surface by a very oblique line. 
Lispacanthus retrogradus, Davis. 
(Pl. XLVIII., fig. 5.) 
Spine, from the base upwards the spine is considerably curved posteriorly, and 
near the apex slightly recurved towards the anterior aspect. It is nearly four 
inches in length, and its greatest diameter at the base 4 of an inch. The breadth 
is gradually reduced towards the apical extremity and ends in a fine point. The 
line dividing the exposed part of the spine from that imbedded in the body of the 
fish extends diagonally across the spine in an extremely oblique direction and 
indicates that the spine extended at a very small angle of elevation along the body 
of the fish, and in all probability was never raised more than a few degrees. The 
whole surface of the spine is smooth; anteriorly it is broad, rounded, with a shghtly 
acuminate ridge along the median line. The sides are depressed, having the appear- 
ance of a wide and shallow groove extending from the junction of the anterior 
portion of the exposed part with the base, to within half an inch of the point. The 
posterior surface possesses a very slight indication of a groove, and leads to the 
impression that the spine was not connected with a fin. The base is imperfect ; it 
is fibrous and was firmly implanted. 
This spine offers several peculiarities which appear to indicate that its relation- 
ship was not with the ordinary types. Its connexion with the body of the fish as 
indicated by the base line, and the absence of a posterior groove for the attachment. 
or accommodation of a fin shows that it was free and possibly only used for offensive 
or defensive purposes; these characters remove it from the Ctenacanthoid type 
The base also differs from the Pleuracanth or Chimeroid types, its oblique implanta- 
tion and wide aperture are quite distinct from the tapermg base and almost 
vertical position of those genera. 
Formation and locality : Mountain Limestone, Armagh. 
Kx coll. Karl of Enniskillen. 
Lispacanthus gracilis, Davis. 
(EL, SOG \WIOUL. seg, Gy) 
Spine, long and tapering, acuminate, gently curved, length five inches, greatest 
breadth at base °4 inch, gradually and evenly contracts in diameter to the apex, which 
is sharply pointed. Transverse section circular, the internal cavity is terminal. 
Surface of spine is smooth, a very slightly projecting keel extends along the anterior 
surface. The posterior surface is devoid of denticles, and so far as can be seen of 
TRAWS, ROY. DUB. SOC.,NS.. VOL. 1 3N 
