GASTEROPODS 



343 



Murex lenuispina. 



Acm&a testudinalis, from below. 



types of marine gasteropods, and their respective characteristics 

 may be noted by comparing them one with another : Fasciolaria 

 tulipa (Plate LXXVI), a Floridian shell; Polynices heros, a com- 

 mon species found on all the sandy shores of the American At- 

 lantic coast ; Murex tenuispina, an Indo-Paciflc species much prized 

 by collectors; and Acmcea testudinalis, commonly found in Maine 

 and Massachusetts at low tide clinging to rocks. 



The extreme top of the shell is called the apex, and it may be 

 either sharply pointed or obtuse. Each turn is called a ivhorl; 

 the last one, and always the largest, is called the body-whorl, the 

 others collectively forming the spire of the shell. When the ani- 

 mal first emerges from the egg it is always provided with one or 

 two whorls, which generally may be distinguished at the apex as 

 smoother than the rest of the spire, and a faint line may be 

 discovered where the shell began its growth after birth. These 



