382 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
Pristicladodus and are described as consisting of a crown composed of one large, 
thick, compressed, sharply-pointed cone, with two denticulated cutting edges, the 
surface lughly polished and either smooth or very finely striated; the base of the 
cone expands at right angles, forming a large semicircular, thick, coarsely osseous 
vase from which there may be extended a single lateral cone on each or not. The 
teeth agree generally with those cf Cladodus in the form of both base and crown, 
the latter, however, differs in the greater robystness of the principal cone, and 
especially in the denticulation of its edges. Prof. M‘Coy remarks, “ The first specimen 
which I saw of this genus I supposed might have been the Carcharopsis prototypus 
of Agassiz’s lists, but subsequently finding a second which was still more nearly 
like Carcharodon, to which he likens his species, I hesitated to identify an un- 
described fossil which I had never seen, more especially as neither of my specimens 
showed any trace of the ridges at the base of the crown alluded to by Agassiz ; 
and the horizontally dilated base was so remarkable a character, totally separting 
them from Carcharodon, and nearly allying them to Cladodus, that I could not 
suppose that the true Carcharops’s prototypus was identical with my fossils, or the 
one resemblance would not have been stated and the other affinity overlooked.” 
Two species are described, P. dentatus, triangular in outline, cone sharply pointed, 
base widely expanded and laterally tapering to a point without cones. This species 
is distinguished from the second one, P. goughi, by the strong, close, deeply-cut, 
regular dentation of its edges, and the deep triangular depression in the anterior 
face. The P. goughi is larger, it has a central and two lateral cones, one on each side. 
In 1866, Newberry (‘‘Geol. Surv. Illinois,” Vol. II., p. 69, pl. VI., figs. 14, 14a) 
described a tooth from the Alabama Limestone very similar to the Pristicladodus 
of M‘Coy. It is recognized as offering a near relationship to that genus, but 
though the name Pristicladodus is regarded as well chosen to indicate the relation- 
ship of the genus, he considered that it was anticipated by perhaps the equally 
appropriate one of Carcharopsis of Agassiz. The latter is therefore retained, the 
tooth being called C. wortheni. 
In 1875, Messrs. St. John and Worthen (“Geol. Survey of IIlinois”, Vol. VI., p. 258) 
amended the genus Pristicladodus of M‘Coy. The P. dentatus of that author is 
regarded as the type of the genus Carcharopsis of Agassiz and P. gought, M‘Coy 
retained as the type of the genus Pristicladodus. The genus Carcharopsis as thus 
amended is described, its principal features being the widely expanded central cone, 
sublenticular in transverse section, the lateral angles sharp and deeply and regularly 
crenulated : extremities occupied by one or two more or less slender, conical lateral 
denticles, which are as isolated as in the case of the typhical Cladodus. The amended 
genus Pristicladodus is characterized by the central cusp being strong, erect, sig- 
moidaliy recurved, rapidly converging to a point, “ lateral edges sharp and more or 
less distinctly undulated or simple : lateral cusps relatively very strong, sometimes 
even more massive than the median cusps, divergent, similar in shape to the median 
