489 CRETACEOUS GASTROPODA 
The geological groups of the South Indian cretaceous deposits have been again 
quoted according to Mr. H. F. Blanford’s report on these rocks in the IVth volume 
of the Memoirs of the Geological Survey; they are, beginning with the lowest, 
the Ootatoor-, Trichinopoly- and Arrialoor-groups, and in addition to these the 
Valudayur group near Pondicherry, in the main features corresponding with the 
lowest group, though the Arrialoor beds (Verdachellum-group) by far predominate 
at this place, and most of the fossils first obtained by Messrs. Kaye and Cunliffe 
appear to have belonged to them. 
All these groups have not yielded an equal number of Gastropoda. When 
speaking of the Cephalopoda I remarked that the largest number had been derived 
from the Ootatoor beds; this is, however, not the fact in the present case; the num- 
ber of Gastropoda obtained from the lowest beds is the smallest and these all appear 
to be littoral forms. This is a very interesting fact, but it would be in vain to 
attempt an explanation of it, until, after examination of the entire fauna, the ground 
shall have been re-examined and the distribution of molluses in the different beds 
compared with the same distribution in the present adjoining seas. 
The majority of the Gastropoda (113 sp.) belong to the Arrialoor beds, being 
deposits in shallow water: next comes the Trichinopoly group with 59, and at last 
the Ootatoor with 86 species; these are peculiar to each group, but a number of 
other species are common to the first and second, or the second and the third. 
There are only 30 species, or very nearly one-eighth of the total (237) number, 
identical with species from cretaceous rocks of Europe and elsewhere; these identi- 
cal species, however, very nearly all belong to the upper beds of cretaceous deposits, 
including the beds from the Cenomanien upwards. Glancing at the entire 
Gastropodous fauna of the South Indian cretaceous deposits its cretaceous 
character could not be mistaken fora moment. This is specially prominent in the 
peculiar forms of the dzar4, the Cerrrampx, Rissoipz, Narierp2, the large num- 
ber of vozuriv” (of the Vorurrpx), the absence of Tursinip%, excepting those 
belonging to the sub-family asrrazrivs, the distinct types of the Przevroromarupsz 
and PyraurpELLips&, etc. The absence of the usual large number of Coyzpa, 
Prevroromipsz, Terese, the nassinz of the Buccrnipz, the urrrivs of the 
Voturims, and others commonly occurring in tertiary beds is very noticeable. 
At the same time it cannot be questioned that there is some approach of our 
fauna to the tertiary one, inasmuch as several types of shells occur which have 
previously not been noticed below the eocene beds, like Cythara, Oniscia, Trophon, 
Pseudoliva, Euclia, Narona and others. I entirely reject, however, the argu- 
ment of some palzontologists, that certain genera are restricted to certain 
formations. It is clear enough that a certain type of Gastropod, which we call 
a genus, must have made its first appearance somewhere, but this is a point which 
experience must settle, or regarding which no statement could have any value, 
excepting so farasit were justified by our experience limited to a certain date. But 
to determine @ priori that a genus does not occur below the tertiary formation, 
and to start with the idea that rocks must be fainozoie because they contain a 
