GASTEROPODA. 



95 



truncated and notched below; but for this it would re- 

 semble Turritella. — Fossil. 



MURCTHSONIA. D'Archiac and De Verneuil. 

 — Shell turret-shaped, usually furnished with 

 keels, or knobs ; aperture oblong, sometimes 

 rounded, sometimes with a short or truncated 

 canal ; the inner lip is mostly curved ; a more 

 or less deep cleft in the outer lip, which has 

 almost parallel edges. — Fossil. 



These shells are very like some of the Pleuro- 

 tomacea. 



Cerithium. Adanson. — Shell turreted, many whorled, 

 elongated, rough and tuberculated ; aperture oblong, obliqus, 

 and having a recurved canal at the base, 

 and a notch at the upper part of the 

 right lip ; operculum small and horny. 

 Animal, head thick and muzzle-shaped, 

 having two awl-shaped tentacula, and 

 eyes on a swollen portion near the base ; 

 foot short and rather triangular. — Above 

 100 species ; also fossil. 



The Mollusca forming these shells 

 chiefly inhabit the Indian and Pacific 

 Oceans, the Red Sea, &c. ; they appear 

 to have the power of remaining for a 

 considerable period out of their natural 

 element, and without food, which is 

 proved by the following fact : — Two 

 specimens containing the animals be- 

 longing to one of the species of this 

 genus, were brought from the Mauritius ; 

 themselves far within the shell, and remained in that 

 state during the voyage ; but on arriving in England and 



Cerithium alum. 



they had drawn 



