GASTROPODA 557 



within the margin; color whitish, yellowish, or reddish, often, banded; 

 length 30 mm.; width 17 mm.: eastern end of Long Island to Green- 

 land, in shallow water on rocks; common, feeding on oysters and other 

 mollusks; Europe. 



FAMILY 2. COLUMBELLIDAE. 



Shell conical, elongate, covered by a periostracum ; aperture narrow, 

 elongated, terminating below in a notch; lip thick, crenulated or toothed 

 within; operculum very small; central tooth of radula 

 without cusps; laterals with 2 or 3 cusps: 1 genus. 



COLUMBELLA Lamarck. With the characters of the 

 family: 300 species, mostly subtropical. 



C. (Astyris Adams) lunata (Say) (Fig. 875). Shell 

 small, with 6 whorls; surface rather flat, smooth, with a Colu'mbella 

 single revolving line and a few near the base; color (Verriii). 

 brownish, with 2 or 3 series of crescentic yellow spots on 

 the lower whorl; length 5 mm.; width 2.5 mm.: Massachusetts Bay to 

 Florida, in shallow water; common. 



C. (Anachis Adams) avara Say. Shell small, with 6 whorls; surface 

 rather flat,, yellowish in color, blotched with brown ; lowest whorl with 

 10 to 15 longitudinal ridges crossed by revolving lines; length 12 mm.; 

 width 5.5 mm.: Cape Cod to Florida, in shallow water; not so common 

 as C. lunata. 



FAMILY 3. NASSIDAE. 



Mud snails. Shell small, conical or ovate, with an elevated spire, 

 thick and solid; aperture round or oval, ending below with a short canal 

 or a notch; columella with a callus; outer lip 

 thickened, toothed or crenate; operculum horny; 

 central teeth of radula with many cusps ; laterals 

 with 2 large and several small ones: 175 species. 

 NASSA Lamarck. Foot square in front, bi- 

 furcate behind or not; operculum with a serrate 

 Fig. 876 Fig. 877 or plain margin: 130 species; cosmopolitan; in 

 Fig. 876 Nassa vibex shallow water; they are scavengers, but are also 



obsoieta (Verriii). predacious, destroying mollusks after the manner 



of the oyster drill. 



N. vibex Say (Fig. 876). Shell conical, with 6 whorls; sutures not 

 impressed ; surface of body whorl with about 12 undulating, longitudinal 

 ridges and 12 revolving lines; color whitish or brown, with a revolving 

 darker band; foot bifurcate behind; length 12 mm.; diameter 8 mm.: 

 Cape Cod to Gulf of Mexico; common south of Cape Hatteras; West 

 Indies. 



