540 MOLLUSCA 



conical, with eyes at their base: several hundred species, in salt, brack- 

 ish, and fresh water, some being- amphibious; they are mostly littoral, 

 and feed on algae, on which they are found. 



Key to the g-enera of Littorinidae here described : 



Oi Shell thick and solid ; no umbilicus 1. Littorina 



Ca Shell thin 2. Lacuna 



1. LiTTOEiNA Ferussac. Periwinkles. Shell conical, thick and 

 solid, with 4 to 6 whorls; lip acute; no umbilicus; foot longitudinally 

 divided, each side advancing alternately when the animal moves; radula 

 2 or 3 times the length of the animal: 175 species, cosmopolitan; in 

 shallow water; more or less amphibious. 



Key to the species of Littorina here described : 

 Oi Shell not smooth and shining. 

 6i Shell with revolving color bands. 



Ci Bands continuous L. litorea 



Ca Bands broken L. irrorata 



62 Shell without color bands L. rudis 



©2 Shell smooth and shining L. palliata 



L. litorea (L.). The edible periwinkle (Fig. 837). Shell not smooth, 

 dark brown, yellowish, or reddish in color, with dark spiral bands; inte- 

 rior white or brown ; length 25 mm. ; width 16 mm. : Europe, where it is 

 an article of food; recently introduced on our Atlantic coast, and now 

 veiy common as far south as Delaware Bay. 



Fig. 837 Fig. 838 Fig. 839 



Fig. 8.37 — Littorina litorea (Leunis). Fig. 838 — Littorina rudis (Verrill). 

 Fig. 839 — Lacuna vincta (Verrill). 



L. rudis (Donovan) (Fig. 838). Shell very solid and thick, with 

 usually spiral ridges and grooves, whitish to red or black in color, with 

 sometimes spiral bands; shell very variable in color and texture; length 

 14 mm.; width 10 mm.: New Jersey to the Arctic Ocean; very common; 

 Pacific coast; Europe. 



L. irrorata (Say). Whorls flattened, yellowish-white or green in 

 color, with numerous revolving ridges which are spotted with short 

 brown lines; throat white; length 25 mm.: Vineyard Sound to Florida, 

 very common towards the south. 



L. palliata (Say). Shell small with a low spire; surface smooth 

 and shining; color yellow, brown, or red, sometimes spirally banded; 

 length 15 mm.: New Jersey to the Arctic Ocean; very common; Europe. 



