186 CRETACEOUS GASTROPODA 
those of the recent Cerithia, did exist in former times, even as far back as the 
jurassic period, can scarcely be questioned ; but we require good materials before we 
can attempt to point out such slight differences, and even in such cases the fossil shells 
must always be carefully compared with those of the living species as regards their 
structure. Only in this way can we arrive at something like a correct determination 
of these forms. 
From the ecretaceous deposits merely a few North American species have been 
referred to Cerithiopsis, like C. Moreauensis, Meek and Hayden (Proe. Acad. Nat. 
Se. Phil. 1860, p. 185), and C. alternata, Gabb (Pal. Calif. 1864, I, p. 116), but 
neither of these species is known in such a sufficient state of preservation as to war- 
rant these determinations. Exteriorly they agree with other well known Cerithiopsis. 
We have ourselves put aside a fragment of an apparent Cerithiopsis from the Arrialoor 
sandstones near Comarapolliam. It isa small sub-cylindrical species with convex 
whorls, spirally striated, and transversally obsoletely costulated. 
XX. Family—CERITHIID 4. 
(H. and A. Adams’ Gen. I, p. 283; Cermruiapax Gray’s Guide, 1857, p. 105.) 
The animals are characterized by a broadly produced annulated rostrum ; 
usually long, subulate, tentacles with the eyes on bulgings or short pedicles at 
their outer base, and by a linear lingual membrane with seven series of teeth, the 
central being single, hooked, and denticulated, the lateral decreasing in size towards 
the outer margins, and all of them multicuspid. The mantle margin has a distinet 
siphonal fold or a slit in front ; the gills are composed of a single series of cylin- 
drical rigid plates. The foot is short, broad, and usually well adapted for sliding. 
Operculum always present, horny. 
The shell is turreted, generally with an elongated spire, and in the recent species 
covered usually with a thin, or in the fluviatile or brackish species with rather a 
rough epidermis ; the aperture is generally channelled in front, or at least distinctly 
effuse : the outer lip often expanded, and externally varicose in adult specimens. 
For many years past paleontologists have drawn attention to the close 
relationship which exists between the shells of the Czrzrazzp% and those of 
PrramipELLip#, specially of Nerinea. Since the establishment of the Czrrruropsipa 
these relations obtained a still firmer basis in consequence of the great similarity — 
of the animals of Cerithiopsis with those of Pyramidella, and, even as regards the 
usually prolonged form of the shell the former genus appears to be closely con- 
nected with the latter. 
We have already, when speaking of the last two families, repeatedly referred to 
these relationships, and thus given expression to our views regarding the classifica- 
tion of the Ceriruip”. The invariable existence of a distinct siphonal fold and 
even that of a short siphon, corresponding usually with a produced anterior canal 
on the aperture, entitles this family fully to the place which we assign it at the 
