358 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
Cosmacanthus priscus, Agass. 
(Pl. XLVIIL, fig. 1, 2.) 
Leptacanthus priscus—L. Agassiz, 1837. ‘ Rech.sur les Poiss. Foss.,” Vol. IIT.,p. 176, indet. 
5 5: J. E. Portlock, 1843. “Geol. Rept. Londonderry, &c.,” p. 461. 
3 3 C. G. Giebel, 1848. “ Fauna der Vorwelt,” Vol. L, pt. 3, p. 306. 
+ 5 H. G. Bronn, 1848. ‘ Nomencl. Paleeont.,” p. 634. 
Nemacanthus priscus—F. M‘Coy, 1848. “Ann. & Mag. Nat. Hist.” 2nd ser., Vol. II., p. 120. 
Leptacanthus priscus—J. Morris, 1854. ‘Catal. Brit. Foss.,” p. 332. 
Nemacanthus priseus— Pa 1854. 35 a oe p. 334. 
Nemacanthus priscus—F. J. Pictet, 1854. “Traité de Paléont,” Vol. IT., p. 286 
Leptacanthus priscus— * 1854. “ x * Vol. II., p. 288. 
es ms Morris & Roberts, 1862. “Quart. Journ. Geol. Soe.,” Vol. XVIII., p. 101. 
Nemacanthus priscus— - 55 1862. 5 3 ‘ 5 Vol. XVIIL., p. 101. 
Leptacanthus priscus—J. J. Bigsby, 1878. ‘Thesaurus Devon.-Carb.,” p. 359. 
Nemacanthus priscus— 5 1878. * 3) 5 $5 p. 359. 
Spine, slightly curved, nearly four inches in length, basal end complete, distal 
one broken off. It is also split in two along the middle, giving a longitudinal 
section and exposing the internal canal, which is round and rather more than one- 
third the diameter of the spine. ‘Towards the base the canal gradually increases 
in size, the walls becoming thinner near the extremity. The base, one inch in length, 
is separated from the exposed part of the spine by a diagonal line extending from 
the anterior margin upwards to the posterior one. The contact of the two sides at 
an acute angle forms an enamelled keel which extends along the anterior 
nargin. The sides are covered by numerous tubercles without definite 
arrangement, the intermediate spaces are covered with a reticulated network of 
minute punctures and lines. 
Spines of the genus Nemacanthus occur in the Liassic formations and bear a 
superficial resemblance to that of Cosmacanthus. Nemacanthus is, however, com- 
pressed and oval in section, and only a portion of the lateral surface is covered by 
tubercles ; whilst in Cosmacanthus the section is triangular, with an inclination 
to roundness. The pulp-cavity is enclosed to a larger extent by the base of the 
spine, and the surface is almost uniformly covered by tubercles. The posterior 
margins in Nemacanthus are denticulated, whilst in the genus under consideration 
there are no denticles. 
The species may be distinguished by the round depressed form of the tubercles and 
the reticulated series of punctures which occupy the spaces intermediate between 
them, and in the indefinite manner in which the tubercles are arranged on the surface. 
Leptacanthus priscus was not described by M. Agassiz, and the genus as 
defined by Prof. M‘Coy (Brit. Palzeoz. Fors., p. 633) 1s quite different to the defini- 
tion here given of Cosn.acanthus priscus. 
Formation and locality : Carboniferous Limestone, Armagh. 
Ex coll. Geclogical Society, London. 
