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Mr. A. R. Hunt. 



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[Apr. 20, 



valve being flat and the other curved it follows that a slight dis- 

 turbance of the water will place it in a stable position. I find that it 

 is quite easy to roll over a full grown P. maximus in my small tank 

 if resting on the convex valve, but to dislodge it when resting on the 

 flat valve transcends the power of any current I can bring to bear 

 upon it. Owing to the rejection by naturalists of the theory of 

 submarine wave-motion, the fact that certain parasitic sea anemones, 

 such as Adamsia palliata and Sagartia parasitica, commonly choose a 

 shell tenanted by a hermit crab (paguncs) has been a matter of some 

 perplexity. But, given the submarine wave action, and the problem 

 finds its solution. The crab keeps the shell from rolling, and the 

 anemone from being killed. I have taken many young specimens of 

 Sagartia parasitica on living shells of Turritella terebra, but from the 

 state in which I have seen shells of this mollusc damaged by rolling, 

 I cannot conceive the possibility of the young anemones having much 

 chance of surviving the first severe storm. The protection afforded 

 by hermit crabs is no matter of fancy, as anyone can see by gently 

 rocking the water in an aquarium, tenanted by hermit crabs, on a 

 sandy bottom. If the crab happens to be in his shell, the first 

 impulse is to dart out his legs and claws, and hold on to the sand on 

 as broad a base as possible. His cousin, the swimming crab (por- 

 tunus), under similar circumstances will burrow, or, if finally dis- 

 lodged by the shifting of the sand, will dart upwards into the water 

 to escape the commotion. Many of the small fishes, crustaceans, and 

 molluscs that frequent the 6-fathom area of Torbay. seem quite on 

 their guard, and prompt in their action when disturbed by oscillating 

 currents in a small aquarium. 



Want of space precludes the possibility of pursuing this branch of 

 my subject further, and compels me to turn to the next question, viz., 

 the evidence afforded by the shells of molluscs of motion on the sea 

 floor. 



I have assumed that wave action on the bottom of Torbay will 

 scarcely be denied, and have passed lightly the evidence of the Torbay 

 shells. It now remains to consider the evidence of those found in 

 deeper waters. Among the shells sent me by fishermen who have 

 taken them on the oyster ground off the mouth of Torbay, in about 

 15 fathoms, have been several specimens of Trochus granulatus, an 

 inhabitant of the coralline zone. On a careful examination of eight 

 of these shells, it appears that not one of them has escaped rough 

 treatment more than once in the course of its life, and that one of 

 them has had to repair serious damages nine times, over and above 

 any slight abrasion that did not suffice to interfere with the sculpture 

 and regular growth of the shell. On the 10th February, 1882, I 

 bought three scallops (Pecten maximus) at a fishmonger's shop, 

 where I was informed they had all been taken .off Berry Head on the 



