THE SLUG AND ITS ALLIES 



169 



shell is about 150 millimetres long, and pear-shaped. In 



one species the margins of the whorls are grooved (Fig. 



157) ; in the 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 Urosalpinx : the canal is short (Fig. 

 158). This typical representative of the 

 Muricidae is everywhere abundant on our 

 Eastern coast. It is much hated by 

 oystermen, by whom it is known as the 

 " oyster drill." It bores through the 

 shell of this and other bivalves by means 

 of its radula and sucks out the contents 

 through the hole. 



Crepidula, 2 the boat shell or " decker," represents a 

 type in which the spire has become almost obsolete. It is 



FIG. 158. Urosal- 

 pinx, the oyster 

 drill. Nat. size. 

 Photo, by W. H. 

 C. P. 



FIG. 159. Crepidula, the boat shell. Two-thirds nat. size. Photo, by 

 W. H. C. P. 



still represented, however, in a rudimentary way at the left 

 of the aperture (Fig. 159). The modified shape is associated 

 with the habit the mollusk has of lying, aperture down- 



1 otpd, tail ; <rd\Triy, a trumpet. 2 A small sandal (crepida). 



