On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 499 
Petalodopsis tripartitis, Davis. 
(Pl. LX., figs. 6, 6a.) 
The genus is represented by this single species, whose characters are those already 
attributed to the genus. The tooth is °5 of an inch across, and about the same in 
height. The crown is ‘35 of an inch high in the centre ; the central cone, or denticle, 
is considerably more prominent than the lateral ones, which gives to the tooth an 
acuminate form. ‘The cutting edge of the outer denticles is slightly serrated, and 
a number of minute striations descend from the crest vertically over the crown, but 
disappear, and give place to a smooth, very finely punctate, enamelled surface. 
Formation and locality : Carboniferous Limestone, Wensleydale. 
Ez coll. William Horne, Esq. 
Genus.—Polyrhizodus, M‘Coy. 
Teeth, strong, transversely elongated. Crown, convex, obliquely elevated, more 
or less oval in outline, and laterally acuminate ; posterior surface of crown, con- 
cave, larger than anterior. Crown separated from base by anterior and posterior 
ridges, with or without imbricating folds; base or root large, deeply implanted, 
oblong, divided into distinct more or less tuberous rootlets or radicles. 
This genus is probably more nearly allied with the Petalodonts than with any 
other group; and it was, no doubt, this external resemblance, combined with, per- 
haps, imperfect specimens, that led Prof. Agassiz, in the year 1840 (“Poissons Fossiles,” 
tome iii., p. 174), to ascribe these teeth to the genus Petalodus (P. radicans). Spe- 
cimens were so named in the collection of Lord Enniskillen and others, but, like 
many other genera and species, were left for description to a future supplement, 
which, unfortunately, has not been written. In a revision of the fishes of the 
paleeozoic rocks, Prof. M‘Coy (“Annals Nat. History,” Second Series, Vol. 11., p. 125, 
1848) published a description of the genus, for which he instituted the name Poly- 
rhizodus. The description was considerably enlarged upon, and specimens of two 
species were figured by Prof. M‘Coy in his “Systematic description of the British 
Paleozoic Fossils in the Geological Museum of the University of Cambridge,” 
page 641, pl. 3k, figs. 2,6, 7, and 8. The Petalodus radicans, Ag., is described under 
the name Polyrhizodus magnus. The second species, P. pusillus, does not appear 
to be a Polyrhizodus, but probably belongs to the genus Helodus. The figures of 
Helodus turgidus, Ag., in the “ Poissons Fossiles” do not represent the root or base of 
the tooth as being divided into fangs or lobes, though one of the figures indicates it 
to some extent; but in the Enniskillen collection, amongst an extensive range of 
the H. turgidus, examples may be selected which show the division of the root even 
to a larger extent than the specimen figured. 
During the Geological Survey of [inois a number of fish remains were discovered 
in the Carboniferous Limestone Series at Burlington and Chester, and amongst 
