52 MOLLUSCA. 
Sept. 1846. Expedition Shells, 22. Prreirrer; Monog. Helic. Viv., 
1. 185. 
AnimaL small, pale, lemon-coloured about the head, pearly white 
posteriorly, obscurely radiated on the side. Tentacles very short and 
small, with a dark line passing behind each one. 
SHELL exceedingly variable in size, form, and colouring. It is 
small, and essentially characterized by its radiating rib-strie, check- 
ered with dusky and yellowish, its seven lamelle revolving within 
the aperture, but above all, by its peculiar umbilicus. In the young 
shell this is broad, conforming to the shape of the spire, the presenting 
edges of the whorls flattened, so as unitedly to form a little cup; but 
as the ‘last whorls are added, the form of the cavity is reversed, its 
diameter diminishing till it is at last nearly covered over, presenting 
only a small opening to the globular cavity, or little purse or pouch, 
its verge being sharp, and in continuation of the lip. 
The shell is small, rather solid, conical or discoid, always marked 
above with more or less coarse, sharp, radiating, rib-like striae; of a 
dusky brown colour, radiately checkered with ashy buff-colour. Be- 
neath, it is either cinereous or mottled with flexuous, radiating pencil- 
lings of brown, with or without radiating and revolving raised strie. 
The whorls are eight in number, closely coiled, carinated, separated 
by a distinct suture which is sometimes margined. ‘The aperture is 
small, transverse, lunate, angular at the periphery; lip simple, and on 
arriving at the umbilicus it bifurcates, and sends a branch each way 
around the perforation, thereby forming something like a vertical 
axial pillar. Of the seven lamelle revolving in the aperture, one is 
on the pillar, rather inconspicuous, two on the penult whorl, and four 
on the outer lip, one above and three below the keel. 
The above characters are found combined in every possible manner. 
The variations in size, colour, solidity, and umbilicus (all the varia- 
tions), may be reasonably ascribed to differences in age and to the 
elevation, between two and five thousand feet, at which they were 
collected 
Two principal varieties may be noted. 
a. Large, elevated, conical, solid specimens which are without mot- 
tling, rib-like striz, or revolving lines beneath. 
Diameter three-tenths of an inch; axis one-fifth of an inch. 
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