158 NASSIDA. 
or longitudinally 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, when adult. N. mwricata, 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. Tritoniformis, 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. Kienert, Desh. (ii, 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, Stimpson. (Ceesia, 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. JN. obsoleta, Say 
(lii, 94). 
The characters proposed by 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 slightly 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 
erabs 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 
