622 J. W. DAVIS ON REMAINS OF FOSSIL FISHES 
angular. The triangular form is similar to that occurring in the 
genus Glyphanodus, excepting its tripartite division. The tooth 
differs also in the semicircular form of its transverse section from 
that of Glyphanodus, which is straight or nearly so. The crown of 
the tooth in Petalodopsis bears some resemblance to that of Pristodus, 
but only a superficial one; it is distinguished from the latter by 
the absence of the horizontal palate, the imbricating folds of the 
surface at the junction of the crown with the base, the small number 
of denticles and the shortness of the root. The teeth of Pristodus 
form each a complete palate, whilst those of the genus now under 
consideration require the combination of several teeth for the same 
purpose. = 
PETALODOPsIs TRIPARTITUS, Davis, l. c. p. 499, pl. lx. figs. 6, 6a 
(1882). (Plate XXVI. fig. 16.) a 
Genus Perret McCoy, Ann. & Mag. Nat. Hist 
ser. 2, vol. ii. p. 125 (1848). s- 
Potyruizopus Core, Davis, l. c. pl. lx. figs. 9, 10 (1882). (Plate 
XXVIIT. fig. 13.) 
Tooth. Small in comparison with the type specimen from Armagh ; 
it is 0-6 inch from the crest of the crown to the tip of the root, 
and 0-8 inch across the crown. The anterior surface is exposed. 
The crown forms an angle of 45° with the vertical axis of the 
tooth, is oval in outline with decumbent lateral prolongations, 
bounded by the cutting-edge and the anterior ridge; the latter is 
prominent and smooth, without transverse folds. The suriace from 
the transverse anterior ridge to the base of the radicles forms a right 
angle with the surface of “the crown, and is about equal in extent. 
The surface of the crown is slightly worn, and has a punctate 
appearance not well defined. The root is divided into five rootlets, 
less than one third the total height of the tooth-rootlets, very 
unegual in size, second and third being apparently double, formed 
by the anchylosing of two rootlets; from the base the rootlets 
extend prominently forward; they are semiglobose, with rounded 
terminations, and apparently about the same diameter laterally as 
antero-posteriorly ; surface coarsely punctate. ; 
The teeth of this species more closely resemble those of P. Colez, 
from Armagh in Ireland, than any others. The principal diffe- 
rences lie in the diminished size of the crown, the great depth 
from the anterior ridge to the denticles, and the shortmess of the 
rootlets as well as their smaller number. So far as can be ascer- 
tained, the specimen from Leyburn is mature; it appears to have 
been considerably worn by attrition, and, if so, it probably belonged to 
a much smaller specimen of the fish than the great teeth of Armagh 
represent ; and it seems probable that it may indicate that the 
genus which flourished and attained its greatest size during the 
period when the Lower Carboniferous Limestone was formed was 
gradually becoming extinct. The thin upper limestones of Wensley- 
