On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 511 
recurved backwards; anterior surface, occasionally much worn by attrition of an 
opposing tooth, is convex transversely, its lateral edges meeting those of the pos- 
terior surface, and forming more or less prominent lateral margins. The basal 
portion of the anterior surface is produced on each side of the median line to form a 
sub-angular prominence, from which the base proper retreats very rapidly, with a 
concave flexure, towards the posterior surface of the tooth. Posterior surface, more 
or less recurved near the apical extremity, concave, and laterally expanded ; separ- 
ated from the base by a sigmoidal curve. The whole coronal surface is enamelled 
and covered with punctures, the latter in some instances near the apex, being con- 
verted into anastomosing canals by the wearing of the surface. Base nearly as lone 
as the crown, coarsely fibrous, extending vertically from the posterior coronal face, 
and with a deep concavity posteriorly. 
A unique specimen occurs in the collection of the Earl of Enniskillen which exhibits 
a series of teeth in situ, showing, at any-rate in part, the arrangement of the teeth 
in the mouth (see Plate LXI., fi. }. The specimen consists of three or four teeth, 
arranged one behind the other, in a very similar manner to those of Petalorhynchus 
or Janassa. The most anterior tooth is the smallest, and the series increases in size 
backwards, the tooth in use being the largest and most recent. By a peculiar arrange- 
ment the anterior sub-angular prominences, from the basal portion of the crown 
already mentioned, fit and are attached to corresponding depressions in the concave 
posterior surface of the preceding tooth. It is probable that five teeth occurred 
in each vertical series, and it is a natural inference that several of these vertical 
rows were extended side by side laterally. 
There are examples of teeth which differ in details of form from the types de- 
scribed above. In some instances the apex is pointed, and the posterior basal 
part ot the crown expanded so as to extend beneath the cone of the succeeding 
tooth (Plate LXI., tig. 5). These do not appear to be such differences as to render 
necessary the formation of a separate species, but may very well have been the 
teeth of either the opposite jaw or from a different part of the same jaw. 
Formation and locality : Mountain Limestone, Armagh. 
zx coll. Karl of Enniskillen. 
Genus.—Ctenopetalus, Agass., MSS. 
Teeth of small or medium size; crown broad, compressed, gently rounded in 
outline ; cutting edge divided into from twenty to thirty small denticles; base 
of crown possessing three or four imbricating folds of ganoine, descending lower 
on posterior than anterior surface; root narrower than crown, flattened, and 
about equal to it in height. 
The genus Ctenopetalus along with that of Harpacodus originally constituted a 
part of the genus Ctenoptychius of Agassiz; they were named respectively 
Cienoptychius (Ctenopetalus) serratus, Ag., and CO. (Harpacodus) dentatus, Ag. 
They were both obtained from the Mountain Limestone; the other species of 
TRANS, ROY. DUB. SOC., N.S.: VOL. I. 41 
