634 BRITISH PALALOZOIC FOSSILS. [ Pisces. 
Length unknown, but upwards of five inches; greatest observed width six lines, at which size the thickness 
is only two lines. 
This species in size, shape, and inconspicuous ridging, agrees perfectly with the Leptacanths of the 
Oolitic rocks. 
Position and Locality—Not very uncommon in the dark lower carboniferous limestone of Lowick, 
Northumberland. 
Explanation of Figures.—P1. 3. G. 14, portion of ray, natural size; imperfect at each end, shewing the 
anterior keel and some of the posterior denticles, and the interruption of the ridges above; fig. 14a, small 
portion of surface magnified, shewing the occasional interruption of the ridges, and the intervening punctured 
strize ; fig. 15, ditto, portion nearer to the distal extremity, natural size; fig. 15 a, portion magnified from near 
the apex, shewing the form of the section, &c.; fig. 16, fragment, natural size, from near the apex. 
Genus. ORACANTHUS (4y.) 
Gen. Char.—Dorsal rays very large, conical, without solid base, hollow from the extremely large internal 
eavity, and thin walls; surface covered with oblique rows of tubercles, or tuberculated ridges; no posterior 
rows of denticles. 
The great size of the internal cavity and consequent thinness of the walls, renders the form of the section 
of these large rays very uncertain. 
ORACANTHUS MILLERI (A4g.) 
Ref.—Ag. Poiss. Foss. Vol. III. t. 3. f. 1 to 4; =O. confluens. Ag. Id. p. 177. 
Desc.—Ray conical, gradually tapering, hollow nearly to the apex; very thin, so that most of the specimens 
are pressed flat, but the long sides of the triangle of such specimens having no fixed relation to the anterior or 
posterior faces ; length of such flattened specimen six inches, width at the base (compressed) two inches nine 
lines ; apex solid with an elliptical section, nearly smooth for six or eight lines from the obtuse point, and then 
ornamented for a few lines more, with small, scattered, oval tubercles, without any order of arrangement, about 
half a line in length; a little lower down the tubercles increase in size, and become conico-pyramidal, nearly 
as high as deep, gradually increasing in size towards the base, near which they become confluent in thick 
undulated ridges ; the lines of separated tubercles on the distal portion of the spine, and the tuberculated ridges 
of the base, are separated by deep concave spaces, minutely striated longitudinally, averaging four ridges in six 
lines on the basal half, about five rows in the same space nearer to the apex; the rows are irregular in 
direction, slightly sigmoid, but have a tendency to meet on the anterior face, in an upward angle of 120°. 
I have examined specimens bearing M. Agassiz’ name O. confluens in the collection of Capt. Jones, 
R. N., M.P., and find they have the characters always assumed by the basal portion of O. Milleri, with which 
they are certainly identical. The extremely puzzling and protean character of the surface, proportions, and 
frequent distortions of this ray are certainly due to its most extraordinary character, which has entirely escaped 
M. Agassiz, viz. the extreme thinness of the substance and great size of the internal cavity; a specimen an 
inch in diameter having a thickness of only one line, so that the whole ray forms a thin, easily compressed, 
hollow cone nearly to the apex, which alone is solid. The tuberculation extends to the extreme edge of the base, 
which has no solid longitudinally striated insertion, like most Ichthyrodorulites. It is owing to this thin hollow 
construction that some specimens are flattened laterally, shewing oblique ridges, and some flattened from 
before backwards, shewing the ridges meeting at a salient angle. This explanation also dispels all the 
difficulties under which M. Agassiz laboured, as to the direction of the ridges, and position of the faces of 
the spine. The ridges pass round the posterior face without marked interruption. I have no doubt the O. 
minor Ag. is the apex of a young specimen of this same species, which might be expected to have the apex 
of very large specimens more solid than small ones, and the tuberculation agrees with that of the apex of a 
moderate sized O. Milleri in the collection, 
Position and Locality —Not uncommon in the carboniferous limestone of Armagh. 
