MARINE MOLLUSCA OF THE UNITED STATES. 37 
Genus PEDICULARIA, Swainson. 
Man. Malacol. 245, 357. 1840. 
Shell very small, limpet-like; with a large aperture, channelled 
in front, and a minute lateral spire. The following species is the 
_ second in the genus, the typical species being a small shell para- 
sitic on corals in the Mediterranean; in the latter there is no 
operculum. The genus is closely allied to Purpura. 
1. P. DEcUSSATA, Gould. 
Proc. Bost. Soc. Nat. Hist., v. 126. 1855. 
Shell solid, variable, generally oval, decussated by radiating 
and revolving striz; apex lateral, obtuse; aperture crescent form ; 
lip thickened, considerably expanded; columella straight, acute, 
sulcate. 
Length 4, diam. 3 mill. 
Dredged at a depth of 400 fathoms. 
Coast of Georgia. 
Genus COLUMBELLA, Lamarck. 
Anim. sans Vert. vii. 292. 1822. 
Shell ovate-oblong, triangular or fusiform; spire acute at the 
apex; aperture long, narrow, contracted in the middle; inner lip 
curved, crenulated or denticulated; outer lip dentate, gibbous, 
thickened in the middle. ‘ 
There are nearly two hundred species of this genus, inhabiting 
temperate and warm seas. They crawl on the surface of sand-flats 
in shallow water, or live on stony beaches, where they congregate 
about and under stones. | 
1. C. AVARA, Say. Fig. 59. 
Journ. Philad. Acad., ii. 230. 1822. 
Shell thick, small, elongate-ovate; spire elevated and acute. 
Whorls six or seven, very slightly convex, almost flat; suture 
distinct. Surface with spiral impressed lines, and vertical obtuse. 
ribs or folds; these latter, consisting of about twelve or fourteen 
in number on the body-whorl, do not descend, beyond the middle 
of that whorl, leaving only revolving lines beneath. Columella 
with a plate of enamel, which is toothed within and truncated 
beheath the margin; lip toothed within. Color whitish, reticu- 
lated or spotted with rufous; often of a yellowish hue. 
Length 12, diam. 4 mill. 
Cape Cod, Mass., to Georgia, 
