GASTKOPODA. 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" {Terehrldce), like the Cones, present a great Cases 



87-89. 



Fig. 14. 



The " Glory-of-the-Sea " Cone {Conus gloria-maris). Case 94. 

 (From the Philii^pine 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 ^^-9*- 



