MARINE MOLLUSCA OF THE UNITED STATES. 37 



Genus PEDICTJLARIA, 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 striae; 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 Qeorgia. 



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 stonj' 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 

 beneath 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, 



