182 MOLLUSCA. 



lowing genera belong to this family : Buccinum, Eburna, 

 Dolium, Harpa, Nassa, Purpura, Cassis, Morio, Ricinula, 

 and Monoceros. 



Family 2. Muricidce. 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. Cerithiadce 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. Strombusidce Canal short, and bent towards 

 the right. The outer margin of the aperture becomes pal- 

 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 by a thick cuticle. It is lodged 

 in a sac, and united by a muscle, which adheres to the pil- 

 lar. The hood is produced, at each side, into a flattened 

 tentaculum, with an eye at the external base. The anus is 



