GASTEROPODS 403 
talium dentale and Entalis striolata. The first has a simple round 
hole at the smaller end of the shell, and is faintly marked by longi- 
tudinal striz; the other is a smooth shell which has a notch-like 
fissure on the margin of the apical perforation. Neither of these 
species is, strictly speaking, a littoral form, for all the Dentalide 
range into deep water, many of them living only in 
the profounder depths of the ocean. But these two s— 
species are exceedingly common in the New England 
coastal waters, at very moderate depths, and may 
sometimes be found upon the beach east up by storms. 
They live buried in the mud, and feed upon infusorians 
and all manner of microscopic organisms. & 
Upon the west coast Dentalium pretiosum is very 
abundant north of California. It is almost like 
the east-coast Dentaliwm, but is more slender. 
The Indians used to gather these shells and string 
them together upon long threads to be carried 
about and used as money. In California oc- g 
curs Dentalium hexagonum, a very delicate 
little species with a slightly angulated shell. 
The animal of the Dentalidw is remark- 7_, 
able, and easily merits the rank of a sepa- 
rate molluscan class. It has no 
head, no tentacles, no eyes, no 
heart, and no gills. Itis a mol- 
lusk because it has a mantle, & —Dentatium, as seen in longitudinal section (ex- 
foot, and aradula. Its position, sovt_th £009: 5 shel: 2, mantle; Sn, shell 
therefore, is between the Gas- voile nemnence or oral nes 7 came 
teropoda, which it resembles in cerebral ganglion; N, kidney; Ge, generative 
its univalve shell and radula, and oe 
the Pelecypoda, to which it is related by the pointed foot and 
the absence of head and tentacles, and also by the symmetry 
which pervades its organization. 
Upon either side of the mouth, just beneath the flap of the 
mantle, are bunches of ciliated, contractile filaments (captacula), 
flattened at the end, which are supposed to be breathing-organs, 
and are perhaps exserted for the purpose of catching food. 
