ATES 
Pisces. | UPPER PALHOZOIC VERTEBRATA. 633 
HoMACANTHUS MICRODUS (J/°Coy). PI. 3. K. fig. 19. 
Ref—M Coy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 115. 
Desc.—Spine about one and quarter inch long, and two lines wide at base; very slightly arched, gradually 
tapering ; section ovate; anterior face formed of a narrow rounded keel, each side with two slightly flattened, 
nearly equal keels, the posterior one dichotomous at its base; they are their own width apart, the intervening 
space being flat and marked with about three longitudinal strise; posterior face with two rows of numerous 
conical hooked teeth, their length scarcely one-fifth the width of the ray at their base. 
The more slender form, flattened ribs and inter-spaces, and numerous small, conical teeth, distinguish 
this from the last, with which alone it is likely to be confounded. 
Position and Locality —Carboniferous limestone of Armagh. 
Lxplanation of Figures.—P|, 3. K. fig. 19, dorsal spine imperfect at each end, natural size; fig. 19a, 
ditto portion magnified. 
Genus. LEPTACANTHUS (49.) 
Gen. Char.—F¥in-spine very long, narrow, gently arched backwards, very gradually tapering, greatly com- 
pressed, sides flattened; anterior face thin, keeled; surface covered with very numerous, close, longitudinal 
ridges and strize, posterior side set with two rows of very numerous, close, small, downward-curved denticles. 
M. Agassiz, in his work on the Old Red fishes, states one of the generic characters of Leptacanthus 
to be a smooth space free of ridges on each side, near the posterior row of denticles; but no such character 
exists in the greater number of his typical species, nor is it alluded to in his former work, where the 
Leptacanthi ave more particularly treated of, except in the case of the common Stonesfield L. semistriatus, 
it being the distinguishing peculiarity of that particular species. 
The genus is Carboniferous and Oolitic. 
LepracaNntHus? JuNcEus (M‘Coy). Pl. 3. G. fig. 13. 
Ref—M Coy, Ann. Nat. Hist. 2nd Series, Vol. IT. p. 122. 
Desc.—Nearly straight, about one and half lines wide: section semielliptical; sides gently convex, meeting 
in front to form a sharp anterior edge, and converging behind to aynarrow posterior sulcus, bordered on each 
side by a row of strong, conical, downward-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 longitudinal striz. 
This is put in Leptacanthus rather than in Homacanthus from the great number and regular delicacy 
of the ridges. 
Position and Locality—Rare in the black beds at the top of the carboniferous limestone of Derbyshire. 
Explanation of Figures.—P\. 3. G. fig. 13, fragment of fin-ray natural size; fig. 13.@, portion of ditto 
magnified. 
LEPTACANTHUS JENKINSONI (1/°Coy). Pl. 3. G. figs. 14 to 16. 
Dese.—Fin-spine 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 fourteen or fifteen subequal ridges, 
ayeraging 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. 
4m 2 
