OF SOUTHERN INDIA. 361 
LIT. Family,—TROCHID. 
The animals of the Yrocuzp# in external form and organisation are almost 
identical with those of the Tvrzinip, the three pairs of filamentous appendages on 
the sides of the operculigerous lobe are generally well developed, and often there are 
one or two additional pairs on the front part of the foot; the head lobes are usually 
small and occasionally wanting; the teeth of many of the genera are, according 
to Philippi, variable within certain limits, though always characterized by the 
large number of uniform laterals. 
Shell conical, pyramidal, with flat, or ovately depressed, somewhat convex 
whorls, spiral lines and ridges generally present, transverse ribs rare; aperture 
quadrangular, occasionally somewhat depressedly roundish, margins posteriorly meet- 
ing at an angle, outer lip sharp at the edge, and very rarely externally thickened, 
immer lip very often terminating with a tooth; operculum horny, circular, consisting 
of numerous narrow whorls, with a central and often somewhat thickened nucleus. 
Until within the last few years hardly more than half a dozen conchologists 
appeared inclined to accept the numerous generic distinctions of Trochus, as pointed 
out by Swainson, Gray, Philippi, H. and A. Adams and others. Still researches of 
late years, having been specially directed towards the careful examination of the 
animals and the relative comparison of the shells, have shown not only the great 
convenience, but in many instances the propriety of the application of distinct generic 
denominations. No attempt, however, has been made to classify the numerous fossil 
species according to the results obtained from the examination of the recent ones; 
and this indeed is not easily accomplished. For as those distinctions are in most 
cases based upon the differences in the columellar lip of full grown and_ perfectly 
well preserved specimens, it will readily be understood that this part of a fossil shell 
very often becomes obliterated by mineral matrix and is very difficultly exposed. 
There is occasionally no less difficulty experienced in determining whether a fossil 
shell be a young or a full grown specimen. 
I shall give a list of the principal so called generic types of this family, append 
ing short characteristics of those which more commonly occur in secondary deposits ; 
of others, which are rarely or doubtfully reported fossil, it will suffice for the present 
to refer to H. and A. Adams’ ‘ Genera’, and other known conchological works. 
To facilitate a review of the genera they might be arranged according to the 
general form of the shells into four sub-families, somewhat similar to those of the 
Tursinip#, though perhaps not equally characteristic. We have representatives of 
all the four divisions in our South Indian cretaceous deposits. 
a. Sub-family,—GIBBULINA. 
Shell depressed, solid, interior margins thickened, generally striated or dentate. 
1. Gibbula, Leach, 1826 (H. and A. Adams, Gen. I, p. 481). Shell conoidal, 
depressed, mostly narrowly umbilicated; aperture angularly roundish, both lips 
internally slightly thickened ; columella sometimes terminating obtusely. 
AU 
