24 THE SHELL-FISH OF THE COAST. 



which, in the living condition of the organism, the 

 tiny white polyps, with their circle of tentacles, 

 may he seen to rise to a height of perhaps a 

 quarter inch or so. Between these tentacular 

 polyps again, which are strictly those elements 

 of the compound organism which secure nutrition 

 to the colony at large, may be found at times a 

 number of smaller bodies, without tentacles, which 

 give origin to, and carry, the egg-capsules, in each 

 of which there are from one to five eggs. Thus 

 does this diminutive colony live in concert, dif- 

 ferent parts administering to the dififerent wants of 

 the assembled multitude. Most of the crusts of the 

 Hydraciinia echinata, for so the polyp is called, are 

 found on the hermit-inhabited shells, but naturally 

 where these have been exposed for too long a time 

 to the dry atmosphere only the crust remains. 



Along with the dog-whelks, we find many of the 

 tide-water pools inhabited by a number of small 

 round-mouthed shells, known as periwinkles or 

 Littorinas, a northern species of which 

 (Liitorina litorea), inhabiting both the 

 American and European coasts, is the 

 common periwinkle of the English 

 markets. These interesting creatures, 

 of which there are three species* on 

 the New Jersey coast, are truly marine 

 ^fc^^wataf in liabit, but still prefer for their habi- 

 tations localities that are only partially 



* Since the above was written Littorina litorea has been found 

 at Atlantic City ; it is a much less elevated shell than the common 

 large periwinkle of our coast (L. irrorata). 



