On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 413 
by interspaces of less breadth. The calcigerous tubes are also wider at their origin; 
they come off not quite at right angles to the medullary canal, but are slightly 
inclined to the grinding surface of the tooth ; they quickly ramify, sending off their 
branches at nearly right angles, and are less flexuous in their course than in the 
Petalodus ; they dilate into angular cells at many parts of the mid-space between 
the medullary canals.” 
M‘Coy (“British Paleozoic Rocks and Fossils,’ p. 621) differs from Profs. 
Agassiz and Owen, and considers that there can be no real affinity between the 
genus Cochliodus and Cestracion or any of the Sharks; for, first, the teeth are 
supported on a strong bony jaw as in Placodus (which also agrees in having three 
teeth on each side of the lower jaw, although differing in microscopic structure) ; 
secondly, the enrollment of the teeth is on the outside of the jaw, and not as in 
sharks, on the inside to allow the succession of teeth from behind forwards; and 
finally, a broken tooth of another species, the C. oblongus, enables me to prove 
the succession of the teeth was not by revolution from behind, as in the Plagio- 
stomous fishes, but vertically from below upwards, as in the Pyenodonts (op. cit., 
pl. 3H, fig. 19 and 31, figs. 28.) Prof. M‘Coy describes four genera, in addition 
to C. contortus, described by Agassiz in the “ Poissons Fossiles,” viz., C. acutus, 
C. magnus, C. oblongus, and C. striatus. These had been previously named by 
Agassiz, but not described (“ Poiss. Foss.,” Vol. IIL, p. 174). The type specimens 
are in the Enniskillen collection. 
The genus Peecilodus, also instituted by Agassiz, was considered by M‘Coy to 
be only a sub-genus of Cochliodus. The number and form of the teeth, with the 
strong inrollment, particularly of the median tooth over the outer part of the jaws 
seeming to be the same in both, “the only tangible difference of the present teeth 
being the more or less distinct longitudinal ridges which cross the teeth parallel to 
the inner margin.” In addition to Pweilodus jonesii and P. transversus, P. obliquus, 
P. parallelus, and P. sublevis, named by Agassiz (“ Poiss. Foss.,” Vol. IIL, p. 174), 
Moy described two others, P. aliformis and P. foveolatus. 
In the year 1858, Prof. Agassiz was led to reconsider and revise his classification 
and arrangement of the Cochliodont group of palates. Since the publication of 
bis great work on fossil fishes, in 1840-3, an immense number of specimens had 
been discovered, and it was, in consequence, possible to form a much clearer con- 
ception of the actual characters and relationships of the several groups forming the 
entire fish-fauna of the Mountain Limestone. The forms, at first considered as 
species of Cochliodus, were not only found to be persistent, but developed 
characters, shewn in largely increased numbers of specimens, which proved their 
several peculiarities to be of generic importance. The result was, that M. Agassiz 
divided Cochliodus and Peecilodus into the genera tabulated in the following list, 
and intended to redescribe the whole group. Adverse circumstances intervened 
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