632 BRITISH PALZEOZOIC FOSSILS. [ Pisces. 
The curiously irregular lumplike figure and quadrate base of the species distinguish it easily from its con- 
geners; the steep striated margin is also peculiar. The puncturing of the surface is rather coarser than that 
of the H. turgidus (Ag.) 
Position and Locality—Rather rare in the carboniferous limestone of Armagh. 
Explanation of Figures.—Pl. 3. K. fig. 4, natural size, shewing the upper surface and part of margin. 
HELODUS TURGIDUS (Ag.) 
Ref—Ag. Poiss. Foss, Vol. III. t. 15. fig. 1 to 12. 
Desc.—Tooth varying in form, but usually unsymmetrically elongate, oval, one of the long sides being 
much more curved than the other; ends abruptly narrowed, depressed, obtusely rounded; middle raised into 
a large gibbosity, which is either obtusely conoidal and very gibbous, or more or less compressed in the direc- 
tion of the length of the tooth, but in all cases obliquely inclined over the straighter of the long sides; surface 
of the medial gibbosity coarsely granulo-punctate, depressed sides nearly or quite smooth. Length of average 
or rather large specimen, one inch; width, five lines; height of crown about the same. 
The obtusely conoidal specimens strongly resemble Chomatodus cinctus, but the concentric, imbricating 
folds at the base of the crown of the one are replaced by the vertical marginal plicze of the root of the other. 
M. Agassiz’ figures, 8, 9 of the above quotation, would probably belong to his so-called species, H. didymus, 
the distinction of which I very much doubt. 
Position and Locality—Not uncommon in the lower carboniferous limestone of Armagh. 
HoMACANTHUS (Ag.) 
Gen. Char.—Fin-spine small, rather rapidly tapering, moderately arched backwards ; sides flattened, con- 
verging to the anterior face, which is obtusely keeled; sides covered with few, very coarse, longitudinal ridges, 
and fine strize in same direction ; posterior margin with two rows of denticles arched downwards. 
This genus differs from Leptacanthus and Ctenacanthus in its small size, and the sides being covered with 
very few, strong, nearly smooth ridges. The genus is by no means a well-defined one, but when confined to the 
two following species, and the Russian Devonian one already published, it has a sufficiently distinct facies. The 
base of insertion has not been observed. 
HomacantTHus MAcropus (M*Coy.) PI. 3. K. fig. 20. 
Ref —M°Coy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 115. 
Desc.—Spine about eight lines long and two lines wide at base, slightly arched and tapering to a point; 
section compressed, trigonal; anterior face formed by a narrow rounded keel ; posterior concave face bounded 
on each side by a large rounded ridge, between which and the anterior keel there is on each side a still smaller 
rounded longitudinal ridge; the two posterior ridges on each side dichotomise near the base; of the two 
intervening spaces, the anterior is rather wider and the posterior rather narrower than the ridges, which they 
separate ; they are concave, and very finely striated longitudinally ; posterior face with twelve or fourteen very 
large, compressed falcate teeth, alternating in two rows, the alternating bases touching, keeled on their convex 
edge, their length nearly equalling the width of the side of the ray at their base. 
The small size, few ridges, and great posterior teeth, easily distinguish this from the other rays of the 
carboniferous period, while the two latter characters easily distinguish it from the H. arcuatus (Ag.) of the Old 
Red sandstone. This genus has not been noted before in the carboniferous period. 
Position and Locality.—Rare in the carboniferous limestone of Armagh. 
Explanation of Figures.—P1., 3. K. fig. 20, dorsal spine natural size ; fig. 20a, ditto portion magnified. 
