GASTEROPODS 403 



fa limn dentate and Entalis striolata. The first has a simple round 

 hole at the smaller end of the shell, and is faintly marked by longi- 

 tudinal striae ; 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 Dentalidce 

 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 cast up by storms. 

 They live buried in the mud, and feed upon inf usorians 

 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 Dentalium, 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- 

 curs Dentalium hexagonum, a very delicate 

 little species with a slightly angulated shell. 



The animal of the Dentalidce is remark- 

 able, and easily merits the rank of a sepa- 

 rate molluscan class. It has no < = *^=^s&}w/v/M/f rF i-ji- nr+ 



i -, ^-7* -=^!3%&rnH: I [^ \\ ** 



head, no tentacles, no eyes, no 

 heart, and no gills. It is a mol- 



lllSk because it has a mantle, a Dentalium, as seen in longitudinal section (ex- 

 font flnrl a vnrJnla Ttc T>ncitir\n ce P* the foot ) : S > she11 ' Mt < mantle; Sm, shell 



ot, ana a raauia. its position, musc i e . Mh mant ie-c a vit y ; F, foot; *,>. 



therefore, is between the GaS- phalic Prominence or oral cone ; T, captacula ; 

 _ R, radula ; D, intestine ; L, liver ; Af, anus ; O, 



. , , , , , 



Which it resembles 111 cerebral ganglion; N, kidney; Oe, generative 



its univalve shell and radula, and g 



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. 



