On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 457 
base, and also in the line dividing the base from the crown being straight, whilst in 
H. triangularis the line follows a deeply sigmoidal curve. 
Formation and locality : Mountain Limestone, Armagh. 
Ez coll. Earl of Enniskillen. 
Helodus expansus, Davis. 
(ESIC IXE RS Hoste lO Os) 
Chomatodus linearis (partim.’ “‘ Ag. Pois. Foss., Vol. IIT., p. 108, Tab, XIT., figs. 5-13. 
Teeth, medium size, quadrato-elliptical, length three or four times greater than 
the breadth, very slightly broader in centre than at the sides. Length, 1:1 inch, 
breadth in centre ‘35 inch. Height of central cone 2 of an inch. Crown, central 
portion produced longitudinally to form an acute ridge, extending along the whole 
length of thetooth; raised in centre to a moderately clevated broad gibbosity. On each 
side, the ridge is slightly broken up into a number of minor very small projections ; 
transversely the central cone and ridge are moderately thin, near the apex expanding 
downwards to form a broad base. Anterior surface, convex laterally, and also from 
apex to base of crown: three or four concentric imbricating folds extend parallel 
with the anterior margin separating crown and base. Posterior surface, deeply 
concave, widely expanded from the central ridge to the posterior margin, along 
which there extends two, sometimes three, imbricating plicee. Lateral margins 
anteriorly, rounded and obtuse, forming a right angle with the posterior margin. 
The anterior and posterior longitudinal plicee are continued round the lateral margins 
in close contiguity. Coronal surface, thickly coated with enamel, covered with a 
very fine reticulation and minutely punctate. Base, equal in depth to the height 
of the crown ; thin, deeply convex anteriorly, less so posteriorly. 
This beautiful species possesses the distinctive characters of Helodus ; the central 
cone is less prominent than usual and the several minor cones presenting a 
denticulated appearance seem to indicate a relationship with Ctenoptychuus. 
Formation and locality : Carboniferous Limestone, Armagh. 
Ee coll. Karl of Enniskillen. 
Helodus rudis, M‘Coy. 
(All, TIX, tmleas Lil, Wiley), 
Helodus rudis—F. M‘Coy, 1848. “ Annalsand Mag. Nat. Hist.,” 2nd Ser. Vol. If, p. 123 
» 5, J. Morris, 1854. “ Cat. Brit. Foss.,” p. 328. 
x . FE. J: Pictet, 1854, “Traité de Paleont.,” Vol. II., p. 267. 
. 33 F. M‘Coy, 1855. <‘‘Brit. Paleoz. Foss.,” p. 631; Pl. 3 K., fig. 4. 
i s Morris and Roberts, 1862. ‘Quart. Journ. Geol. Soc.,” Vol. XVIII, p. 100. 
96 ” J. J. Bigsby, 1878. “Thesaurus Devonico-Carb.,” p. 357. 
Teeth, “irregularly oblong, subquadrate ; sides, steep, irregularly uodulose, or 
undulate-plicate ; crown irregularly gibbous, the highest point a little nearer one 
end than the other; surface polished, coarsely punctured. Length, seven lines ; 
width, four and a half lines ; height, two and a half lines,’—J/‘Coy. 
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