624 BRITISH PALAZOZOIC FOSSILS. [ Pisces. 
CocHLIODUS STRIATUS (Ag. name only). PI. 3. I. fig. 27. 
Dese.—Terminal tooth aliform, triangular, very much broader than long ; long articular margin forming an 
angle of about 35° with the outer edge; along this articular margin is the most prominent part of the surface, 
forming an obtusely rounded, slightly sigmoid ridge ; the remainder of the surface being flattened and extending 
with a slight concavity to the terminal point, which is nearly rectangular, and obtuse. Surface with a fine, 
sharp, granulo-punctation, having the usual quincuncial arrangement on the long, obtuse convexity of the 
articular ridge, and on the opposite, flattened, terminal angle; but on all the intermediate portion the 
puncta fall into regular, slightly flecuous lines, extending longitudinally nearly at right angles to the articular 
side; about twelve of the lines of punctures in the space of one line. Length of tooth at right angles 
to articular ridge three and half lines; length of articular ridge, or greatest width of tooth, seven lines. 
I only know the terminal wing-shaped teeth of this species, the smallest fragments of which are easily 
recognised by the striated appearance of the surface under the lens, owing to the linear disposition of 
the puncta. 
Position and Locality—Rare in the lower carboniferous limestone of Armagh; very rare in the dark 
lower carboniferous limestone of Lowick, Northumberland. 
Explanation of Figures —PI. 3. 1. fig. 27, natural size, terminal tooth, viewed from above; fig. 27 a, 
portion of surface of ditto, magnified; fig. 27 4, sketch of smaller perfect specimen (in collection of 
Captain Jones, R.N., M.P.). 
Genus. CTENACANTHUS (Ag.) 
Gen. Char-—Fin-spine of moderate and large size, compressed, gradually tapering, moderately arched 
backwards; anterior face narrow, rounded ; posterior face concave, with a moderate cavity, the lateral edges 
bordered by two rows of curved denticles inclined downwards. Surface marked with strong, longitudinal 
ridges and furrows, pectinated by transverse scales or tubercles. The concealed base of moderate size, 
rapidly tapering, finely striated. 
The fin-defences of this genus are confined to the Devonian and carboniferous rocks, where they 
seem to represent the genus Hybodus of the Mesozoic strata. They are distinguished by the decussation 
of the ridges of the surface. 
CTrENACANTHUS CRENATUS (Ag. name only). PI. 3.1. fig. 31. 
Desc.—Fin-spine gradually tapering, moderately compressed; sides rather flattened, converging to a 
narrow, rounded, anterior, face; each side with about ten or eleven nearly equal, regular, rounded ridges, 
separated by sulci, about their own width apart, (at six lines wide there are five ridges in two lines) each ridge 
with a row of small transverse tubercles, strongly crenating the sides, down which they extend obliquely ; 
those of each side usually opposite, but sometimes subalternate, generally leaving the middle of each ridge 
smooth, but occasionally in some spots the small tubercles from each side of a ridge meet on the middle, 
forming transversely rhomboidal tubercles, attenuated at the lateral extremities ; five lateral tubercles in the 
space of one line. The posterior cavity is rather large. 
The length of this species is unknown, but it is probably at least four inches.. The species is easily 
recognised by the regular ridges being crenated, or milled like the edge of a coin, by the small elongate 
tubercles projecting at right angles from the sides of the ridge, and usually not encroaching on its centre. 
Position and Locality —V ery rare in the carboniferous limestone of Armagh. 
Explanation of Figures.—Plate 3. 1. fig. 31, fragment, natural size; fig. 31 a, ditto, section; fig. 31 4, 
portion of surface magnified. 
