GASTROPODA. 21 
Tertiary strata have been described. The typical forms are charac- 
terized by a slit in the outer side (lip) of the aperture. Species 
of Pleurotoma are found in every sea, although most abundant in 
the tropics, and, although so numerous in species, the number of 
specimens is small in comparison with some other genera. 
The "Auger-shells" (Terebridm), like the Cones, present a great ^2^ 
Fig. 14. 
The " Glory-of-the-Sea " Cone (Conus gloria-maris). Case 94. 
(From the Philippine Islands.) 
similarity in form, but, unlike them, have a great diversity of " sculp- 
ture " or external ornamentation. They are all elongate shells, with 
a deep notch at the base of the aperture. Owing to the length and 
comparative solidity of the shells, the animals of many of the species 
do not carry their shelly structures on their backs, like most other 
species, but drag them along the sandy sea-bottom. 
The Conidce, or Cones, form one of the most beautiful portions of Cases 
the collection of Shells. This family, of which between 400 and 500 89 ~ 94 
