CRETACEOUS FISHES. 363 
tions ; the teeth of this species are sometimes very large, but they vary ex- 
ceedingly in size. The smaller ones are difficult to distinguish ; the sharpness 
of the large folds of enamel is the most striking character. This species occurs 
both in the upper and lower chalk ; the finest specimens I have seen are from 
Kent. I had a specimen from Kent containing eighty-four teeth of this species, 
many of them so different in their appearance, that if they had been found singly 
they would have been difficult to determine ; I have now a group from Southeram- 
pit, near Lewes, of upwards of fifty teeth of this species; it is found also in 
France, Germany and Italy. 
Ptychodus paucisulcatus, new, R. 2. (Tab. XXX. fig. 3.) 
Having seen many well-marked teeth in which the great folds of enamel are 
large and very few in number, I am induced to form a new species, for which 
I propose the name of paucisulcatus. This tooth is nearly square ; the great folds 
of enamel seldom exceed six or seven in number, and are larger and stronger 
than in P. latissimus or any other species ; they do not extend to the margin ; 
the accessory denticles, or small folds of enamel, are finer than in P. latissimus 
or P. polygyrus. Mr. Catt has a specimen of this species containing 147 teeth, 
none of them differing from the specific characters here given. The specimen 
figured by M. Agassiz, plate 25 b. fig. 26, appears to belong to this species. 
Ptychodus polygyrus, C. (Tab. XXX. fig. 9; Tab. XXXI. fig. 10. 
Vol. iii. p. 155, Agassiz.) 
I have found this species most frequently in the lower chalk. The principal 
folds of enamel are curved in a greater or less degree at their extremities, and in 
some specimens form complete circles. The small folds of enamel have a con- 
centric arrangement. The furrows between the principal folds are more shallow 
than in P. latissimus, and the folds themselves smaller and not so elevated. Mr. 
Catt had a group found near Lewes containing 213 teeth of this species. 
Ptychodus depressus, new, C. (Tab. XXXI. fig. 9.) 
There is often seen in cabinets a large tooth somewhat resembling those of 
P. polygyrus, but the great folds of enamel are smaller and extend nearly to the 
edge of the tooth; it has no elevation in the centre, but is quite flat, this cha- 
racter not being attributable either to age or usage. I propose the name of 
depressus for this species. In the British Museum there are several examples 
of this tooth ; it may also be seen in most collections of chalk fossils. 
