On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 351 
‘The specimen described by Prof. M‘Coy, as Leptacanthus junceus, consists of a 
small fracment of a spine from the black beds of shale, above the Mountain Lime- 
stone of Derbyshire. It appears to be unique, and is in the collection at the Wood- 
wardian Museum, Cambridge. The following is Prof. M‘Coy’s description of it :— 
“Nearly straight, about one and a half lines wide; section semi-elliptical ; sides 
gently convex, meeting in front to form a sharp anterior edge, and converging behind 
to a narrow posterior sulcus, bordered on each side by a row of strong conical down- 
ward-curved teeth, little longer than wide, and about the width of their bases apart ; 
each side with about seven longitudinal, narrow, equal, thread-like ridges, twice 
their diameter apart, and having between each pair two or three obsolete longitu- 
dinal striz.” This is included in Leptacanthus rather than in Homacanthus, from the 
great number and regular delicacy of the ridges. 
Formation and locality: Black Shale above Limestone, Derbyshire. 
Lz coll. Woodwardian Museum, Cambridge. 
Acondylacanthus jenkinsoni, M‘Coy. 
(JP, SOU WIL, ste, 3) Dey, 
Leptacanthus jenkinsoni—F. M‘Coy, 1855. “Brit. Paleoz. Foss.,” p. 633, pl. 3 G, figs. 14-16. 
= 5 Morrisand Roberts, 1862. “Quart. Journ. Geol. Soc.,” Vol. XVIIL., p. 101. 
fs i. Young and Armstrong, 1871. “Trans.Geol. Soc.,Glasgow,” Vol. III., supt., p.72. 
» ‘ Armstrong, Young, t 1876. 
66 (54. - UR “x, 9 
amndl RG Sanco, Catal. West. Scot. Foss.,” p. 62. 
“ Fin ray, very long, slender, tapering at the rate of one line in two inches, very 
much compressed ; sides flattened ; anterior face surmounted by a strong keel. 
Sides with about 14-16 ridges, averaging six in two lines; about twenty ridges 
when six lines wide, and about ten, when two lines wide, (in the latter case near 
the apex, a smooth band runs along the posterior edge), separated by narrow, 
shallow sulci; ridges often inconspicuous, and singly interrupted or discontinued 
at irregular distances; both the ridges and sulci obscured by a longitudinal, 
slightly irregular striation, posterior edges set with very numerous and very small 
much-hooked denticles, nearly twice the width of their bases apart, three in three 
lines, at four lines wide. Length unknown, but upwards of five inches ; greatest 
observed width six lines, at which the thickness is only two lines.”— (M/‘Coy.) 
Transverse section, the sides are straight, bending over anteriorly, and joining to 
form a median acutely-pointed carina ; posteriorly a shallow sulcus, is bounded by 
acute latero-posterior angles with denticles. Internal cavity large, sub-lenticular, 
laterally and anteriorly conforming to the shape of the outer surface, posteriorly 
produced in the centre, and approaching near to the surface of the posterior sulcus ; 
base, if any, unknown. 
The specimens figured by Prof. M‘Coy are in the collection at the Woodwardian 
Museum, Cambridge, and, together with the one now given (Pl. XLVL., fig. 2), form 
the entire number of specimens known. 
TRANS. ROY. DUB. SOC., N.S., VOL. I. 3M 
