25 2 Shell Life 



central teeth have three or more strong cutting 

 points, or cusps, whilst the side teeth are plain. It is 

 to the skilful manipulation of these 

 central teeth that those neat round 

 holes in bivalve shells are due, the 

 members of this family being mostly 

 carnivorous. A further character of 

 these mollusks is seen in the shells, 

 the mouth running off into a spout, 

 as shown more clearly in the figure 

 sting-winkle ^f ^^XQ Ribbed Spindle-shcll (Trophon 



Ocmehra ermacea ^ ^ . ^ 



triincatus). This spout is for the 

 accommodation of the siphonal fold of the mantle, 

 and is commonly referred to in handbooks as the 

 anterior canal. Through the siphon fresh 

 supplies of water are drawn into the 

 branchise. It is worthy of note that as a 

 rule (to which there are several notable 

 exceptions) this form of shell and siphon 

 indicates carnivorous propensities, and the 

 reason for its existence may be found in the 

 habits of the creature. Much of the food 

 of these mollusks is tainted, often putrid ; and whilst 

 the mouth is immersed in such a pabulum it would 

 clearly not serve the purpose of respiration to draw 

 in water from the immediate neighbourhood. The 

 long siphon is extended to one side, or over the top 

 of the shell, and the water taken in from as remote a 

 point as possible. 



The Little Spindle-shells (Troplion) are represented 

 by three species, of whelk-like form, all being about 

 two-thirds of an inch long. The Prickly Spindle- 

 shell {T. muricatus) is slender, dull, the whorls 



