40 LECTURES ON MOLLUSCA. 



spirally grooved. The umbilicus (or pierced pillar) is generally spiral, 

 leaving a lump on which the apex of the operculum lies when open. 

 The remaining genera have horny opercula. The northern species 

 mostly belong to the group Lunatia, with straight umbilicus and 

 small pillar-lump. In Neverita, which is found in subtropical regions, 

 the spire is flattened, the mouth wide, and the umbilicus winds round 

 a lump which more or less fills it up. This lump is sometimes grooved. 

 The shells of Polinices have the spire conical, and the umbilicus nearly 

 covered by a very large flattened lump: they are white, or only 

 slightly tinted. Arrtpuuina, of which only one species is living, the 

 rest abounding in the Eocene, has a ventricose shell, with the axis not 

 perforated. It is polished by the very large foot, and there is a large 

 lump on the pillar. Naticella has a thin, open shell with very small 

 umbilicus, almost covered by a narrow, dark colored deposit. In the 

 form of the shell, it passes into Sigaretus, in which the shell is flat- 

 tened, sometimes ear-shaped, and partially concealed by the animal. 

 The outside, however, is striated, not polished as in ordinary Naticas. 

 The operculum is very small, and the animal sluggish and timid. 

 Naticina is intermediate between Naticella and Sigaretus, having an 

 umbilicus but no lump. Amaura is a boreal form, with raised spire 

 and solid pillar. 



In the families which follow, the teeth are arranged in different and 

 peculiar patterns. The shells are of very dissimilar shapes ; but the 

 animals all agree in having a retractile proboscis. 



Family LAMELLARIAIXE. 



In this family the foot is enormously large, completely enveloping 

 the shell. There is a slit in the mantle to convey water to the gills. 

 The shell is flat, transparent, or horny. The teeth are in rows of 

 three, as in the Muricids ; but the side teeth are very large and trape- 

 zoidal. The Coriocella is a large black animal, inhabiting the tropical 

 seas. Lamellaria and Ermea are principally from temperate regions. 

 In Ermea there appear to be additional lateral teeth. 



Family SCALARIAD^I. (Wentle Traps,) 



The Dutch called these shells Winding-Stairs, from the beautiful 

 step-like rings ascending in a spiral. The spire is more or less eleva- 

 ted, with a round mouth and reflexed lip, which leaves a varix at each 

 period of increase. Sometimes the whirls are separated from each 

 other, only adhering by the edge of the rings. This is beautifully 

 seen in the famous Scalaria pretiosa, for which the Dutch used to give 

 two hundred dollars, but which may now be bought for one. The 

 animal has a fold in the mantle to convey water to the gills, being the 

 foreshadowing of the siphon-pipe in the canaliculated shells. The foot 

 is extended in front, grooved behind, with a thin, spiral operculum. 

 The head is crescent-shaped, and armed with a strong, fleshy trunk. 

 When disturbed, the creature emits a purple dye. It is very vora- 

 cious, eagerly devouring putrid meat. The teeth are quite different 

 from those of all other prosobranchiate mollusks, resembling most 



