CRETACEOUS FISHES. 365 
lines of enamel diverge from the central ridge, more regularly on one side than 
the other; the shape is curved, and it has a thick base. In the centre of the 
jaw the teeth are probably larger ; but it is a well-marked species. I have drawn 
this description from a small tooth in my own cabinet, found at Washington. 
Teeth of the same species are also preserved in Mr. Coombe’s and Mr. Catt’s 
collections. 
Genus Cestracion!, Cuvier. 
Cestracion canaliculatus, Egerton, R.4. (Tab. XXXII*. figs. 8 & 8*.) 
The discovery of a species of true Cestracion in the chalk is an event of much 
interest, since this genus has hitherto only been known from the recent Cestra- 
cion Philippi or Port Jackson Shark, a fish most valuable to paleontologists as 
being the only existing type of the family Cestraciontide, so extensively dis- 
tributed through our fossiliferous strata, from the Silurian to the chalk both 
inclusive. The specimen proving the former existence of this genus in the 
cretaceous ocean belongs to the Marquis of Northampton, and was found in 
Kent. It fortunately shows both the anterior prehensile and posterior molar 
teeth ; the former closely resemble those of the recent species in form, but they 
are longer in proportion as compared with the molars ; the latter in the fossil 
are narrower, their surface rougher, and the central ridge higher, in the latter 
respect resembling the teeth of Acrodus. The most striking specific character 
occurs in the disposition of the medullary canals traversing the base of the 
teeth. These in the recent species are irregular in size, two or three being larger 
than the others. In the fossil one large canal is constant, traversing the base of 
each tooth, and forming, when they are in juxtaposition, a continuous passage 
through the entire range ; the margin of one aperture of this canal in each tooth 
is produced, and corresponds with a depression on the adjoining tooth,—a 
mechanism very similar to the articulations of the scales in the Ganoid fishes. 
The arrangement of the teeth also differs from the recent species ; in the latter 
the teeth before and behind the principal row diminish in size, but in the fossil 
we find a row of small teeth between two rows of larger ones. As far as the 
evidence of Lord Northampton’s specimen goes, this species was much smaller 
than the Cestracion Philippr. 
' kéorpa malleus, dcous dens. 
3B 
