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 genera of Littorinidae here described : 



o t Shell thick and solid ; no umbilicus 1. LITTOBINA 



o a Shell thin 2. LACUNA 



1. LITTORINA 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 : 

 Oj Shell not smooth and shining. 

 Z>! Shell with revolving color bands. 



c t Bands continuous L. LITOREA 



c, Bands broken L. IBBORATA 



6 a Shell without color bands L. BUDIS 



c, 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 

 very common as far south as Delaware Bay. 



Fig. 837 Fig. 838 Fig. 839 



Fig. 837 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. 



