212 MOLLUSCA. 
Axial diameter four and a half to five inches; transverse diameter 
four inches. 
Inhabits Oregon, at Discovery Harbour, Puget Sound. Pickering. 
This certainly exceeds in size all other species yet discovered. It 
is allied to N. heros, some specimens of which occasionally approach it 
in size. It is, however, less globular, and distinguished by the re- 
markable constriction near the suture. Specimens were brought from 
the mouth of the Columbia, by Lewis and Clarke, and have been 
designated by the above name. 
Figure 253, vertical view of the shell; 253 a, the operculum. — 
Nartica caurina (Gould). 
Testa parva, solida, levigata, globoso-ellipsoidea, albida, epidermide tenut 
stramineo induta, viz perforata: spira obtusa, erosa, anfractibus 
quatuor cum dimidio, ultimo sub-tabulato, anticé subcontracto : 
apertura parva, semilunaris ; columella recta, postice callo coptoso albo 
indutda. 
Natica caurina, Goutp; Proceed. Boston Soc. Nat. Hist., 11. 239. 
July 1847. Expedition Shells, 50. 
SHELL small, solid, smooth, of a round-ellipsoid form, of a dead, 
dirty milk-white colour. Whorls four or five, the upper ones forming 
a depressed spire, with the apex eroded, and suture linear; the last 
whorl very large, full posteriorly, and somewhat tabular at the suture ; 
the last whorl is quite as long as broad, and perhaps attenuated at 
base. The aperture is about two-thirds the length of shell, semilunar ; 
the outer lip sharp, the pillar lip straight, heavily and broadly loaded 
with callus posteriorly, and regularly narrowing, and yet nearly 
covering a small umbilical pit at the middle, so as to leave merely a 
small, linear chink, or none at all. 
Axial diameter half an inch; transverse diameter two-fifths of an 
inch. 
