LamnaP [tooth]

Odontaspis sp. [tooth]

It has been pointed out by Messrs. Newton and Jukes-Browne
that the common species of Desmoceras which occurs in the Mam-
millatus Bed near Folkestone is apparently very closely related
to D. beudanti (Brongn.), but that it differs by having a rather
more complex lobe-line, as regards finer details, and also by the
fact that it always has a series of constrictions 1 . Numerous

1 E. T. Newton and A. J. Jukes-Browne, in Jukes-Browne. ' The Cre-
taceous Rocks of Britain, vol. i., Gault and Upper Greensand' (Mem. Geol.
Surv.), 1900, p. 443.
FOSSILS OF MAMMILLATtJS BEtl : DOVER. 101

specimens found in this bed at Dover all belong to the ligated
form, and are identical with the ammonites found at the same
horizon at East Wear Bay, Folkestone, to which Messrs. Newton
and Jukes-Browne drew attention. Those authors decided to re-
gard this form as a variety of D. beudanti, and they proposed to
call it D. beudanti, var. ligatus. They state that D. beudanti,
while occurring in the Gault above, has not been found in the
Mammillatus Bed ; and although it has been quoted as one of the
fossils from the Mammillatus Zone at Wissant 1 , there does seem
to be some doubt whether it made as early an appearance as the
ligated form with which we have to do at Dover and Folkestone.
There is, therefore, some degree of probability that this ammonite
has been classified as a " variety " of a species which appeared
later. Moreover, the choice of the name ligatus is unfortunate,
and in the event of specific rank being accorded to this form the
use of the name would be certain to introduce confusion with
d'Orbigny's Ammonites ligatus, likewise a Desmoceras.
