IIORN-SII ELLS. 
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form, spheroidal ; surface, smoothisli ; operculum, 
horny; umbilicus, large. It somewhat resembles 
the similar species, Natica clausa , Brod. & Sby., 
which may be distinguished by its closed um- 
bilicus and shelly operculum. 
The black, corkscrew-like shell shown in Fig. 
2, PI. VI, which we may call a Horn Shell, is 
known by the name of Cerithidea sacrata , Gld. 
There are ten whorls, numerously ribbed, with a 
deep suture between them. This shell contrasts 
strangely with the moon-shell, the greater part 
of that being the body whorl, while there is 
little to this except the spire. The outside is 
dull black ; the inside, glossy brown. Length, 
one, to one and a half inches. Unlike the pre- 
vious species, this one delights in the brackish 
waters of bays and marshes. The writer gather- 
ed them in great numbers on the muddy fiats at 
the head of Lake Meriitt, in Oakland, where 
they seemed to be enjoying the fresh air, after 
the tide had left them on the surface of the mud. 
Some similar species in other countries spend so 
much time in the air that they have been mis- 
taken for land shells. Owing to their form, 
they are very difficult to clean. • After boiling, 
as much of the soft parts as possible should be 
removed, and the space plugged with cotton, to 
which the horny, circular, multi-spiral opercu- 
lum should be attached by a drop of glue. 
Bittium filosum, Gld., Fig. 3, PI. VI, is a 
little, brownish, spiral shell, living in the sea, 
and marked by spiral grooves, without ribs. It 
is a bout half an inch long, strong and solid. 
