242 
THE GEOLOGIST. 
in the Mautell collection. The teeth have not been found in any 
strata more recent than the "Wealden. As far, therefore, as the 
evidence goes, it seems much more likely to be of an age anterior to 
the Cretaceous system." This, then, is at most only doubtfully a Cre- 
taceous species ; and the only other instance of which we have any 
published figure or description is the Hylodus sulcatus referred to by 
Sir Philip, and recorded in Morris's " Catalogue," on the authority 
of Agassiz (vol. iii, p. 44, t. 106, fig. 15, 16), as from the chalk of 
Lewes in Sussex. All Agassiz says is, "M. Mantell possesses two 
fragments of rays of a Hybodus found in the chalk of Lewes, but 
which are in a bad state of preservation. One recognizes, however, on 
the surface the furrows and the longitudinal ridges, characteristic of 
Syhodus, which present this particularity, that they are very straight 
(droites) and very uniform. At the posterior edge one distiuguishes 
a well-marked longitudinal ridge (fig. 16a), which constitutes a spe- 
cific character sufiiciently defined to permit the founding of a species 
upon such imperfect pieces. I have not seen any teeth on the pos- 
terior sides ; I doubt not, how^ever, that such existed, but they have 
probably been broken, which does not appear astonishing in frag- 
ments so damaged." These two fragments, little more than an inch 
each in length, are now in the British Museum ; and a careful inspec- 
tion has convinced me that grains of Wealden grit still adhere 
to them, and, therefore, that they can no longer be regarded as even 
Cretaceous still less as Chalk specimens. No Chalk fossils were ever 
seen of such a peculiar nature as the substance of which they are 
composed. There remain, then, to retain Hyhodus as a Cretaceous 
species, only those relics, whatever they are, which Professor Morris 
has recorded as " species : Chalk, Northfleet (Collection Wetherell) ; 
Norfolk (i?05e)," and which have never yet been figured nor described.* 
Very great interest, therefore, attached itself at once to a small but 
very fine and delicately-preserved jaw, with numerous teeth, to which 
my attention was drawn, in the National Collection (No. 36908). 
It is from the Lower Chalk of Dover. The extreme length of the 
right ramus of the lower jaw is 2i inches ; its vertical depth at the 
middle and deepest part, | of an inch ; and the depth of the upper 
and lower jaws together, 1^ inch. There are twenty-five teeth in all, 
fully visible, and fragments, may be detected of one or two more. 
* Mr. Rose informs me that the reference in Morris's Catalogue is to a specunen in 
his collection identical with the ichthyodorulite figured in Dixon's ' Geology of Sussex,* 
tab. xxxii. fig. 7, which, however, is not Hybodus. Mr. Rose's specimen is from the 
Lower Hard Clialk of ^Vhittington, near Stoke Ferry, West Norfolk. What the speci- 
mens in Mr. Wetherell's collection are we do not know. — S. J. M. 
