GASTEKOPODA. 



71 



these shells were rare in cabinets ; and though they are 

 now oftener seen, they are by no means very common. 



Leptoconchus. Ruppell. — Shell, sub-globular, deli- 

 cate, fragile, translucent; spire low, 

 and nearly effaced by the encroachment 

 of the last whorl ; aperture large, and 

 in form somewhat like the letter S 

 reversed ; the two margins not united ; 

 the right delicate at all ages, and a 

 little expanded; no columella or um- 

 bilicus. Animal, with a lengthened, but 

 entirely retractile proboscis ; the mouth Leptoconchus. 

 appears to be unarmed ; two flat, short, 

 triangular tentacula, which are connected at the base, and 

 have the eyes about half way up, on the outside ; the foot 

 moderate ; the mantle has a circular edge, with a slight 

 prolongation on the left side ; the gills are furnished with 

 a single comb. — 1 species. 



The shell of this genus is of a dirty milk-white, fur- 

 rowed externally. It is found in the Red Sea, where it 

 is embedded in calcareous masses of Polyparia, having 

 no communication with the water except by a moderate 

 opening. 



Purpuroidea. Lye. — (Pur- 

 purina D'0?'b.) Shell ventricose, 

 with a wide mouth and an acute 

 spire, composed of several, gene- 

 rally convex, coronated, or thorny 

 whorls; the columella smooth, 

 roundly curved, inclined inwards 

 towards the base ; the notch at the 

 base broad, shallow, not curved 



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