GASTROPODA 537 



FAMILY 1. NATICIDAE. 



Shell usually globose or flattened, with a short spire; aperture round 

 or lunar; lip sharp; umbilicus open, or closed by a callus; operculum 

 usually corneous; foot very large and capable of being swollen by the 

 taking in of sea water into open spaces and reflected back over the shell 

 so as almost to cover it; tentacles small, lanceolate, wide apart, united 

 by a veil; eggs deposited in a "sand collar," a thin collar-shaped lamella 

 formed by agglutinating grains of sand together by means of mucous: 

 several hundred species. 



Key to the genera of Natiddae here described : 



ttj Shell globose 1. NATICA 



a a Shell flattened with a very large aperture. 



6 t Shell ear-shaped 2. SIGABETUS 



5 a Shell trumpet-shaped 3. VELUTINA 



1. NATICA Lamarck. Shell smooth and regular, gray or brownish 

 in color, with about 5 whorls; eyes wanting; umbilicus usually more or 

 less closed by a large callus: over 200 species; predacious animals, liv- 

 ing in the sand, where they burrow after bivalves; they envelop their 

 prey in the foot and penetrate its shell, drilling a hole with the radula; 

 they also devour dead fish; about 20 species on the Atlantic coast. 



Key to the species of Natica here described : 

 G! Shell over 25 mm. long. 



&! Umbilicus wide and deep N. HERDS 



6, Umbilicus nearly closed by a brown callus N. DUPLICATA 



a. Shell 15 mm. or less long. 



&! Umbilicus wide and deep N. IMMACULATA 



6 a Umbilicus more or less covered by a white callus. 



Ci Shell 8 mm. or less long N. PUSILLA 



c a Shell over 10 mm. long. 



di Shell with minute revolving lines N. GROZNLANDICA 



d a Shell without revolving lines N. CLAUSA 



N. (Polynices Montfort) heros Say (Fig. 

 831). Shell large and moderately thick; whorls 

 5, convex; umbilicus large and deep; length 9 

 cm.; diameter 8 cm.; shell ash color, streaked 

 with chestnut: Virginia to Labrador; from low- 

 water mark to 238 fathoms; common. 



N. (Polynices Montfort) duplicata Say. Shell 

 solid, whorls 5, flattened above; spire low; color 

 ashy gray, tending towards brown on the upper 

 side, chestnut brown within; callus very large, 



chestnut brown in color, almost filling the umbilicus; length and 

 diameter 5^2 cm.: Massachusetts Bay to Mexico; common in shallow 

 water. 



