456 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
Helodus richmondiensis, Davis. 
(itl, IDIDX,, ters, 8, Sat.) 
Teeth, small, median cone triangularly rotund, with shght lateral prolongation ; 
diameter at the base °3 inch, height -2 inch. Crown abruptly elevated to a 
prominent cone with a slightly acute apex; the anterior surface convex, with a 
median ridge extending midway between the two lateral ones from the summit to 
the base. . Posterior surface deeply convex longitudinally, transversely rotund. 
Posterior surface separated on each side from the anterior one by a well-defined, 
straight ridge, descending from the apex of the cone to its base; one of the ridges 
is prolonged at its base, and forms a lateral process extending beyond the median 
cone. Coronal surface covered with enamel, uniformly and deeply punctate. Base 
hidden by the matrix. 
This tooth bears a close resemblance to Helodus simplex, Ag., from the coal 
measures. The form of the central cone is similar, the principal difference con- 
sisting in the absence in H. simplex of the well-defined and peculiar ridges 
descending from the summit of the crown to the base. The lateral prolongations 
of the crown in H. simplew are somewhat more extended than in this species. 
Formation and locality : Carboniferous Limestone, Richmond, Yorkshire. 
Ex coll, Earl of Enniskillen. 
Helodus triangularis, Davis. 
(Pl. LIX., figs. 9, 9a, 96.) 
Teeth, transverse section approximately triangular and consisting of a single 
cone. Height, -4 of an inch, about equal to the antero-posterior diameter and a 
little less than the lateral diameter near the base. Summit of cone obtusely pointed 
and slightly curved backwards. Anterior face convex, separated from the base by 
a sigmoidal curve, the median part of it extending from the antero-lateral angles, 
half the length of the tooth, towards the point. The anterior surface forms at its 
junction with the posterior one angular lateral ridges extending from the apex to 
the base. The posterior surface is doubly concave, with a wide and prominent 
median projection separating it into two parts, and expanding towards the base so 
as to render the form of the tooth almost that of a triangle. Eneircling the base 
of the crown there is a series of imbricating folds, very irregularly arranged. The 
coronal surface, smooth, enamelled, or minutely punctate; where worn, near the 
apex, the surface is occasionally roughly pustulate. Base not known. 
This species approaches most nearly to the type of H. simplex, Agass., from the 
coal measures, in possessing a single cone and comparatively small base, but it 
differs materially from that species in its transversely triangular form, in its pointed 
apex and the minute punctation of its enamelled surface. 
Helodus vichmondiensis is distinguishable from this species by. the presence ofa 
well-defined process or ridge, extending from the apex along the median line to the 
