ns 



ZOOLOaT 



other they are carried out into thorns. The egg-cases are tough 

 and membranaceous and resemble rows of coin strung on a string, 

 the whole being slightly coiled. 



In U'rosalpinx ^ the canal is short (Fig. 

 207). This typical representative of the 

 murexes is e\'erywhere abundant on our 

 Eastern coast. It is much hated by 

 oystermen, by whom it is known as the 

 " oj'ster drill." It bores through the shell 

 of this and other bivalves bj^ means of its 

 radula and sucks out the contents through 

 the hole. 



The muddy bottoms of protected 

 marine harbors are occupied by the mud- 

 snail (Nassa), whose canal is a mere notch 

 through which the very long siphon can 

 be extended. The long siphon enables 

 it to draw in pure water \vhile its body is embedded in the 

 mud. This burrowing serves either as a 

 protection from predaceous species or pre- 

 vents desiccation -svhen the fiats are left 

 uncoA'ered liy the retreating of the tide. 

 One may often see Nassas grou]Ded in solid 

 masses around the body of some dead mol- 

 lusk. They are attracted toward the food 

 by a marked chemical sense, and thej^move 

 toward the source of any current that con- 

 veys particles that stimulate this sense. 



Fig. 200. — Shell of Fid- 

 gur (Sycotypus) canic- 

 ulatus, one of the 

 F asiol aritUe. One- 

 fourth nat- size. Photo, 

 by W. H. C. P. 



Crepid'ula,- the boat shell or " decker," 



^ oura, tail ; salpinx, a trumpet. 

 ^ A small sandal (crepida). 



Fig. 207. — Urosal- 

 pin.x, the oyster 

 drill. Nat. size. 

 Photo, by W. H. 

 C. P. 



