THE TOOTH SHELLS 

 Class Scaphopoda 



Shell tubular, tapering, curved, open at both ends; i to 5 

 inches long; body elongated, curved, symmetrical, attached to 

 shell by muscles near posterior end; mantle lines shell, forms 

 tube which flares at anterior end; surface absorbs oxygen, acting 

 as organ of respiration ; head rudimentary; eyes none; foot long, 

 pointed; mouth at base of foot contains radula; filaments for 

 seizing food are grouped at corners of mouth; stomach and intes- 

 tine simple; liver large, two-lobed, much-branched; kidneys, two, 

 large; reproductive gland large, much elongated in posterior end 

 of shell, discharges through right kidney; sexes separate; heart 

 rudimentary, one-chambered; arteries none; gills none; brain a 

 very small ganglion, connected with four others. Food, small 

 infusorians and other microscopic organisms. Habitat, sandy 

 or muddy sea bottom, from shallows into very deep water. 

 Distribution world-wide in seas. Shells used for money and for 

 personal adornment by primitive tribes. 



Family DENTALiiOi^ 



Foot partially enclosed by a fleshy sheath, which is cleft 

 into two terminal lobes; shell tusk-shaped, ribbed, strong, like 

 ivory in texture. 



The most important family in the class. It includes a 

 single genus of about one hundred and fifty living species. 



Genus DENTALIUM, Linn. 



Characteristics of the family. 



The Dentalium burrows into the sand of the ocean floor, 

 until it lies, head downward, in a slanting position with the little 

 end of its shell thrust up into clear water, and the mantle spread, 



299 



