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NASSARIIDAE 237
part of the Gulf of Mexico, specimens often have a weak keel on the
shoulder (form or subspecies plagosum Conrad).
Busy con coarctatwn Sowerby Turnip Whelk
Yucatan area, Mexico.
Plate I a
Until 1950 this was considered a very rare species, but dredging activities
of shrimp trawlers have brought a large number of them to light. Characterized
by its turnip-like shape, single row of numerous small, dark-brown
spines, and by its golden-yellow aperture. 5 inches in length.
Family NASSARIIDAE
Genus Nassarms Dumeril 1806
Subgenus Nassarms s. str.
Nassarms vibex Say Common Eastern Nassa
Cape Cod to Florida, the Gulf States and the AVest Indies.
Plate 2 3q
% inch in length, heavy, with a well-developed parietal shield. Last
whorl with about a dozen, poorly developed, axial ribs which are coarsely
beaded. Color gray-brown to whitish with a few splotches or broken bands
of subdued, darker brown. A common sand or mud-flat species. Some
specimens have numerous weak spiral cords. Parietal shield sometimes yellow-
ish.
Nassarms acjitus Say Sharp-knobbed Nassa
West coast of Florida to Texas.
Figure 53c
Ya: inch in length, characterized by its glossy shell, its strong, pointed
beads, and in occasionally having a narrow, brown, spiral thread connecting
the beads. Moderately common. Fossil specimens are twice as large.
Nassarms insculptus Carpenter Smooth Western Nassa
Point Arena, California, to Lower California.
Figure 53f
% inch in length, outer lip thickened, parietal wall thick, white but
not very wide. Body whorl smoothish, except for weak, fine spiral threads.
Axial ribs numerous only on early whorls. Color white, covered by a yellow-
ish white periostracum. Moderately common; dredged from 20 to 200
fathoms.