On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 597 
there are eight radicles preserved, two pairs being anchylosed. The spaces between 
the radicles are narrow in front, but expand to a greater width behind. The sur- 
face of the rootlets or radicles is indiscriminately pustulated or reticulated. Where 
fractured they show a close and fibrous texture. 
This tooth is altogether dissimilar to any other species. It appears to be consi- 
derably worn by attrition along the surface of the crown; but it is not probable 
that its deep circular lateral concavity has been formed by the surface being worn 
away in this manner. 
Formation and locality : Carboniferous Limestone of Armagh. 
Ex coll, Earl of Enniskillen. 
Genus.—Chomatodus, Agassiz. 
“Teeth, transversely much elongated, compressed and depressed. Crown having 
the homologous parts of Petalodus, and the form and structure of Polyrhizodus— 
root short, sometimes obsolete, undivided.”—(Worthen. ) 
In 1848 Prof. M‘Coy added two new species to the genus Chomatodus, described 
in the Annals and Mag. of Nat. Hist., Vol. IT., p. 115, as C. obliquus and C. den- 
ticulatus. Six years later his work on the British Paleozoic Fossils was published, 
in which (p. 617) after describing the general characters of Chomatodus, he writes, 
«This genus has, I think, no claims to be retained : the blunt-coned, thick species 
(as C. cinctus, &c.) might be advantageously classed with Helodus, most of the species 
of which, with the same form and punctured surface, have more or less perfectly 
developed imbricating folds at the base of the crown; and the thin unpunctured 
species with a cutting edge belong to Petalodus (Owen), in which the folds always 
exist. I use the genus here for some intermediate types provisionally, and for 
Agassiz’s species.” 
Prof. M‘Coy very accurately attributed little importance to the occurrence of a 
greater or smaller number of concentric folds around the base of the teeth, from 
which Agassiz instituted the genus Chomatodus. Such folds are present on a con- 
siderable number of genera, and in no way serve to distinguish them from each 
other. Of the three species of Chomatodus described and figured by Prof. Agassiz, 
the third C. acuminatus (Pois. foss., Vol. IIL, p. 108, Tab. 19, figs. 11, 12, and 13), 
is without doubt a species of Petalodus. It is an unique specimen discovered by 
Sir R. Murchison, in the limestone at Whorlton in Durham. Agassiz observes 
(op. cit., p. 159) that this species must be eliminated from the genus Chomatodus, 
because of its trenchant cutting edge, and placed with the Hybodonts, or more pro- 
perly with the sharks (Squalides) properly so called. It will be included in the 
new genus Petalodus of Owen. 
The second species C. cinctus, Agass., appears to be entirely composed of teeth 
which are indistinguishable from Helodus or Lophodus, and are now included in 
one or other of those genera. 
