158 NASSID^, 



or longitudmally plicate ; inner lip with the callus sharp, straight, 

 defined ; outer lip produced in the middle, variced externally. 

 N. maculata, A. Adams (lii, 88). 



PHRONTis, H. and A. Adams, Spire elevated, acuminate, 

 whorls ribbed or nodulous, distinctly shouldered ; inner lip 

 smooth, with an extended, thickened callus, outer lip with an 

 external varix. N. luteostoma, Brod. and Sby. (lii, 89 \ 



HEBRA, H. and A. Adams. Whorls spinose, muricated or 

 sharply tubercular ; inner lip with the callus defined ; outer lip 

 with a marginal varix, Avhen adult. N. muricata^ Quoy (lii, 90). 



HiMA, Leach. (Tritonella, A. Ad.) Spire elevated, whorls 

 cancellated ; inner lip with a rugose callus, callus defined ; outer 

 lip with a marginal varix. N. Triloni/ormis^ Kiener (lii, 91 ). 



NiOTHA, H. and A. Adams. Shell cassidiform ; spire short, 

 whorls granulated or cancellated ; inner lip with the callus very 

 large and spreading ; outer lip crenate, not variced externally. 

 N. Kieneri^ Desh. (lii, 92). 



TRiTiA, Risso. (Uzita, H. and A. Adams.) Spire elevated, 

 whorls reticulated ; inner lip smooth, with the callus moderate ; 

 outer lip simple, not variced. N. trivittata^ Say (lii, 93). 



ILYANASSA, Stimpsou. (Csesia, H. and A. Adams. Schizopyga, 

 Conrad.) Shell dark olive-brown, reticulated, outer lip without 

 varix, striate within, columella covered with a spreading callus. 

 Operculum with entire (not serrated) margin. Animal having a 

 broad foot, not bifurcated behind as in Nassa. N. obsoleta, Say 

 (lii, 94). 



The characters proposed b}^ Stimpson include an operculum 

 without serrated margin, and the animal without posterior bifur- 

 cation. Although the operculum is usually serrated in Nassa^ 

 Mr. Marrat has enumerated a dozen species in which it has been 

 observed to have plain margins, or nearly so ; and Dr. von Mar- 

 tens states that the European N. reticulata is found in the mud- 

 flats of the Venetian lagunes with the operculum plain on one 

 side and somewhat serrated on the other, and that the end of the 

 foot is but slightl}^ notched in these specimens instead of being 

 deeply bifurcated. Under these circumstances, it becomes very 

 doubtful whether the group Ilyanassa ought to stand. I have 

 concluded to retain it provisionally, especially as it may include 

 several species conveniently separable from Tritia by having 

 dark-colored shells. 



The animal of the common American species, N. obsoleta^ Say, 

 is variously mottled with slate-color, the tentacula are suddenly 

 diminished above the eyes, and become bristle-like. Its move- 

 ments are very active, and it collects in numbers about dead 

 crabs and other marine animals, on which it feeds. Inhabits all 

 our muddy shores, preferring situations not exposed to the surf 

 of the open sea; such as inlets and extended flats which are 



