498 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britaan. 
it is only -2 inch, the imbricated folds occupy nearly three-fourths of its surface. 
Anteriorly the crown is covered with a coat of dense enamel, through which the 
dentigerous tubes do not appear to penetrate unless it be at the apex, along the 
serrated edge they may be distinctly seen where the serrations are worn off. Root, 
anterior surface, from the ridge is depressed and concave, lower portion convex 
roughly fibrous, posteriorly it is convex and rounded with a number of vertical 
ridge-like prominences. The root conforms to the general shape of the crown, it 
is deepest on that side on which the crown is highest, and in the opposite direction 
gradually converges and meets the coronal surface, forming a slightly acutely- 
pointed termination. 
This species of Petalodus is different in general characters to any other known from 
the limestone strata of Great Britain. In breadth of the crown and small vertical 
extent it somewhat resembles Petalodus rectus, Agass., but in the unequal develop- 
ment of the two sides of the teeth and the number of imbricated folds separating 
the crown from the base, it is quite distinct. It might be considered that this 
peculiar form of tooth was due to its position as a side tooth in connexion with 
other species of more regular form, were it not that it is confined to one locality in 
the upper strata of the Limestone series of Yorkshire, whilst in the districts in 
which the ordinary form of Petalodus is found P. inequilateralis is absent, so that it 
is improbable that such can be the case. 
In some respects this species appears to occupy an intermediate position between 
Petalodus and Chomatodus; its thin sharp crown with serrated apex allies it to 
Petalodus, whilst its great proportionate breadth and wide extent of surface 
occupied by the coronal foldings resemble Chomatodus. The root is, however, 
much more largely developed, more tumid and rounded than in Chomatodus. 
Formation and locality ; Limestone, Wensleydale, Yorkshire. 
Ex coll. Earl of Enniskillen. 
Genus.—Petalodopsis, Davis. 
Teeth, medium size, strong. Crown, laterally strongly arched, smooth, 
acuminate. Crest constitutes a sharp cutting edge, divided into three similar 
denticles; centre one largest, with a deep sulcus on each side separating it from the 
two lateral ones. Crown separated from root by a coronal band consisting of four 
or five imbricating folds of ganoine, straight in the middle, bending downwards on 
each side. Root descends from crown, as in Petalodonts; strong, tapering down- 
wards, inbevelled; not so wide or deep as crown. 
The affinities of this genus appear to be with the Petalodonts ; the sharp cutting 
edge ot the tooth, and the well developed base or root, are clearly related to that 
group. It appears to hold an intermediate position between Petalodus and Petalo- 
rhynchus ; it is separated from the former by its tricuspidate crown, and from the 
latter by the smallness of the root, absence of palate and paucity of denticles. 
