182 MOLLUSCA. 
lowing genera belong to this family: Buccinum, Eburna, 
Dolium, Harpa, Nassa, Purpura, Cassis, Morio, Ricinula, 
and Monoceros. 
Family 2. Muricide.—Canal produced, and_ straight. 
The tentacula approach the head and mouth as in the pre- 
ceding family. The genera are Murex, Typhis, Ranella, 
Fusus, Pleurotoma, Pyrula, Fasciolaria, Terebra, Triton- 
alia, and Turbinella. 
Family 3. Cerithiade—Canal short and recurved. Head 
with a hood. This family contains the marine Cerithium 
and Strutheolaria, and the fluviatile Potamidum, Melanop- 
sis, and Pirena. 
Family 4. Strombuside.—Canai short, and bent towards 
the right. The outer margin of the aperture becomes nal- 
mated with age, and exhibits a second canal, generally near 
the former, for the passage of the head. The following are 
the genera: Strombus, Pterocera, Hippocrenes, and Ros- 
tellaria. 
2d Tribe. 
Shell internal. 
This tribe consists at present of only one genus, termed 
Sigaretus, two species of which are natives of Britain. The 
foot of the animals belonging to this genus, or rather of the 
species which constitutes the type, is oval, with a duplica- 
ture in front. The cloak is broad, with an indentation on 
the left side, in front, leading to the branchial cavity. A 
ring of transverse muscles unites the cloak with the foot. 
On the back is placed the shell, which does not appear on 
the outside, as it is covered byathick cuticle. It is lodged 
in a sac, and united by a muscle, which adheres to the pil- 
lar. The hoed is produced, at each side, into a flattened 
tentaculum, with an eye at the external base. The anus is 
