On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 349 
and doubt that they can be separated. The Armagh specimen differs from the 
American ones in being smaller, and somewhat shorter in proportion to its breadth. 
Both the species named differ from A. tuberculatus, in possessing a much larger 
number of lateral costze, and in the latero-posterior denticles being blunt and obtuse, 
short, and more widely separated. The coste, also, nearest the anterior margin are 
tuberculose, whilst those of the Armagh specimen are quite smooth and simple. 
Formation and locality : Mountain Limestone of Armagh. 
Ex coll. Karl of Enniskillen. 
Acondylacanthus distans, M‘Coy. 
(IRL 2GbNWAL, wiles, 5.) 
Ctenacanthus distans—F. M‘Coy, 1848. ‘Ann. and Mag. Nat. Hist.,” 2nd Ser., Vol. II., p. 116. 
45 J. Morris, 1854, “Cat. Brit. Foss.,” p. 323. 
s = F. J. Pictet, 1854, “Traité de Paléont.,” Vol. IT., p. 290. 
Bs ss F. M‘Coy, 1855. “Brit. Paleoz. Foss.,” p. 625, pl. 3k, fig. 15. 
Morris and Roberts, 1862. “ Quart. Journ. Geol. Soc.,” Vol. XVIIT., p. 100. 
“Spine, compressed, gently arched, very long, slender, tapering at the rate of 
only three lines in five inches; posterior face with two rows of numerous, small, 
short, conical compressed teeth, slightly bent downwards, rather more than the 
width of their base apart ; sides flattened with about ten or twelve close, flattened, 
longitudinal ridges of irregular width, the broadest occasionally subdividing as they 
approach the base, all the ridges crenulated by small tubercles, about double the 
thickness of the ridge from each other; those on the anterior ridges are transverse 
and slightly oblique, while those nearer the concave margin are smaller, and 
assume the appearance of lengthened nodulose swellings as in Physonemus. 
“This is a remarkably long and slender ray ; one specimen in the University 
collection, of which a considerable portion of the apex must be lost, measures six 
inches in length, and only six lines in width at the broadest part near the base, 
the broken distal extremity being three lines wide, which would probable indicate 
a further inch and a half of length. The portion of the base inserted in the flesh 
is small and gradually tapering. I am not certain of the exact form of the 
section,’ —(M‘Coy.) 
This species is in every respect, except that the longitudinal ridges are crenulated 
and not smooth, a good example of the genus Acondylacanthus. In the Enniskillen 
collection, though there is a large number of specimens, there is not one with the 
basal portion perfect, and it may be inferred that the Ctenacanthus type of base 
with a wide, open, posterior sulcus did not exist; if it had—and other examples of 
that genus may be taken as guides—some of the specimens would have had the base 
preserved. It rather appears probable that the opening was terminal, and that a 
very small portion of the spine was embedded in the flesh. The two species named 
