Pisces. | UPPER PALAZOZOIC VERTEBRATA. 629 
Genus. GLOSSODUS (A1/°Coy). 
Ref.—MCoy, Ann, Nat. Hist. 2nd Series, Vol. II. p. 127. 
Dese.—Tooth tongue-shaped, oblong, quadrangular, much higher than wide; crown elevated, slightly 
recurved, narrowing from the base to a small subtruncate apex; surface porous, puncta generally seeming con- 
fluent towards the apex; punctured surface terminating below in a notch, or arched line, the convexity 
upwards ; root long, as wide as the crown, coarsely fibrous. 
The Glossodi are distinguished from the Helodi, with which alone they have any affinity, by the quadran- 
gular form of the horizontal section of the tooth, the sides being flattened as well as the anterior and posterior 
faces ; also by the great height of the crown in proportion to its width. The long root-like base of the tooth, 
which resembles that of some Petalodi (e.g. P. psittacinus Ag. MSS.) rather than that of Helodus in form, 
is of an open lacunose structure, being permeated by very large, flexuous, medullary canals, producing irregular 
openings on the surface. The ridge separating the punctured surface from the base forms a sinus directed 
upwards, which is the reverse of what we find in Petalodus, approaching the ordinary sharks, and also conform- 
ing to what we see in Helodus and Strophodus, when the separating line in those genera is not straight. As in 
Petalodus, the basal margin of the surface is much nearer the apex on the convex anterior side than on the 
concave posterior or internal face, the latter being generally about twice the length of the former. 
The characters above given as distinguishing those teeth from the Helodi also separate them from the 
genuine Petalodi of Owen, as also the want of the imbricating folds at the base. 
GLOSSODUS MARGINATUS (J/°Coy). PI. 3. K. fig. 1. 
Ref—MCoy, Ann. Nat. Hist. 2nd Series, Vol. II. p. 128. 
Desc.—Crown about one-third higher than wide, having a slight antero-posterior sigmoidal curve; thick- 
ness from before backwards, little more than one-fourth of the width; lateral margins subparallel, prominent 
on the posterior face, which is gently concave in the middle; apex narrowed, rounded, curved backwards ; 
surface glossy, finely punctured, marked towards the tip with minute anastomosing longitudinal wrinkles; a 
few obtuse plicee. Length of crown five lines, width three lines. 
Easily distinguished from the G. lingua-bovis by its more finely-punctured, glossy surface, rounded tip, 
and prominent lateral margins. 
Position and Locality.—One of the rarest fossils of the carboniferous limestone of Armagh. 
Explanation of Figures —PI. 3. K. fig. 1, natural size; fig. 1 @, ditto magnified. 
Genus. GYRACANTHUS (4g.) 
Gen. Char.—Fin-spines very large, gradually tapering to the apex, and slightly arched backwards ; inserted 
base small, rapidly tapering; posterior margin feebly armed with two rows of small denticles; surface of the 
sides covered with very oblique rugged ridges, which meet at an angle on the anterior face. 
The genus is confined to the carboniferous rocks. 
GYRACANTHUS OBLIQUUS (A/°Coy). Pl. 3. K. fig. 13, 14. 
Dese.—Dorsal ray nearly straight, about one foot long, and one and a quarter inch wide at base; section 
heart-shaped, width two-thirds of the antero-posterior diameter; anterior face narrow, rounded ; posterior face 
broad, concave, having near the apex a row of small hooked teeth on each side; sides slightly convex, marked 
with numerous very oblique crenulated ridges or rows of tubercles, which meet the anterior face at an angle 
of about 35° (those of opposite sides meeting at an angle of 70°); the ridges become gradually more oblique, 
smooth and entire near the apex; they are about half a line in width and slightly more than their own diameter 
apart. The line of separation between the ridged external surface and the finely striated part which enters 
the flesh is very oblique and with a slight sigmoidal curve. 
