38 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
grove swamps, and the mouth of rivers; they are so commonly out of the 
water as to have been taken for land-shells. Mr. Adams noticed them in 
the fresh waters of the interior of Borneo, creeping on pontederia and 
sedges; they often suspend themselves by glutinous threads. (Tryon, 
Structural and Systematic Conchology .) 
Type. Cerithidea decollata Linnaeus. 
Distribution. India, Ceylon, Singapore, Borneo, Philippines, Port 
Essington, Pacific Coast. 
Cerithidea californica Haldeman, 1840 
Monograph of the Freshwater Mollusca of the United States , cover of No. 1. 
Epidermis thin, glaucous, under which the shell is chocolate colored, 
often with a central narrow white band; longitudinally ribbed, and oc¬ 
casionally thickly varicose, crossed by spiral ridges, the crossings varying 
from nearly smooth to roughly tuberculate; apex usually entire. Length, 
1.25 inch. (Tryon, Manual of Conchology , 9: 162; PI. 33, figs. 65, 66.) 
Range. Baulinas Bay to San Diego, California. 
Family TRICHOTROPIDAE 
Genus TRICHOTROPIS Sowerby, 1829 
Testa univalvis, turbinata, carinata, tenuis, apertura longitudinem spire 
superante, basi integra, columella ad basim oblique truncata, labio externo 
tenuissimo acuto. Epidermis cornea, super carinas testae erinacea. Oper¬ 
culum corneum, lamellis ellipticis confertum, nucleo laterali. 
The shell may be characterised as being turbinated, and carinated 
externally; its aperture is wide, but still longitudinal, and it is rather 
longer than the spire; its base is entire, without any notch, although im¬ 
mediately below the obliquely truncated base of the columella there is an 
indistinct canal. The whole shell is thin and delicate, its outer lip particu¬ 
larly so. Epidermis horny, forming numerous sharp-pointed bristle-like 
processes on the edges of the carinse outside the shell; very strong and by 
its contraction in drying frequently breaking the edge of the lip. Oper¬ 
culum horny, much smaller than the aperture, composed of elliptical 
laminae, its apex or nucleus lateral. (Sowerby.) 
Type. Trichotropis borealis Gould. 
Distribution. Circumboreal. Fossil, Cretaceous. 
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