OF THE UNITED STATES. 243 



the basal portion of that part is more dilated than the 

 quoted figure of that species. It is possible, however, 

 that it is only a variety of that species. 



TURRITELLA, Lam, 



Species. 



1. T. *alternata. Shell dusky ; acute at the apex $ 

 volutions eight, with about eight unequal, revolving, 

 slightly elevated lines, which are maculated with 

 rufous, and decussated by transverse, elevated, obtuse 

 lines, which are obsolete below the middle of the 

 body whirl and prominent on the spine! ; labrum not 

 thickened, a slight indentation at its base. 



Length one-fifth of an inch. 



Inhabits the coast of the United States. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



Animal — Foot longer than the aperture of the 

 shell, rather acute behind, and truncated a little con- 

 vexly before ; tentacula filiform, cylindrical, obtuse 

 at tip, nearly as long as the foot, white, annulate 

 with brownish lines ; eye at the external base of the 

 tentacula, not prominent; rostrum about one-third 

 the length of the tentacula ; operculum blackish. 



The shell when taken from the water, becomes 

 whitish-cinereous. They abound amongst Fucus, 

 and sometimes on the shell of Limulus Polyphemus. 

 The animal considerably resembles that of tetania 

 Virginica as respects form, and, in common with 



