[huntsman] INTERTIDAL ANIMALS 



55 



that exists from low tide level downwards and the uniform column 

 shown has been marked off into five fathom intervals. Above low 

 water datum a figure has been constucted, which terminates at an 

 apex corresponding in height above low water mark, as shown by the 

 scale in feet on the side, to the highest level reached by the water. 

 The width of this figure at any level in reference to the width of the 

 basal column is equivalent to the percentage of the total time that 

 such a level is covered by water. The sides of this figure are almost 

 straight. 



The distribution of the periwinkle {Littorina litorea) was observed 

 to be between the levels of five and twenty- two feet above the low- 

 " water datum; that of the barnacle {Balaniis halanoides) between 

 four and twenty-two and one-half feet; and that of the mussel {Mytilus 

 edulis) between four and one-half and seventeen feet. These are to 

 be considered as extreme limits, the zone of abundance for each 

 species being more restricted. The distribution that has been given 

 was observed on the sides of the wharf and not in such special situa- 

 tions as tide-pools. 



The sea-urchin was met with at as high a level as nine and one- 

 half feet above low-water, but only under special conditions. On 

 the north side the wharf rests on a ledge of rock not far above low- 

 water, and on this ledge protected from the sun the sea-urchins were 

 able to rest at low tide. When the tide rose, they moved slowly 

 up the side of the wharf, some of them attaining the level we have 

 mentioned before the falling tide exposed them to the air and induced 

 them to relax their hold on the wharf to fall again to the ledge below. 

 In dredging in this region we have obtained the sea-urchin at various 

 depths down to more than thirty fathoms. The whelk (Buccinum 

 undatum L.) has a distribution quite similar to that of the sea-urchin, 

 but reaches a level of only about six and one-half feet above low water! 

 It moves to a higher level at spring tides than at other times, and is 

 able to remain at such heights without harm at the time of low tide 

 by frequenting soft beaches or mussel beds, in which it can bury 

 itself and escape the heat of the sun. The star-fish {Asterias vulgaris) 

 is to be found from depths as great as thirty fathoms up to a level of 

 eight feet above low water mark. In the figure (1) we have shown the 

 distribution of all these species graphically beside the column repre- 

 senting the water. 



At Cheticamp or Eastern Harbour, N.S., on that shore of Cape 

 Breton island bordering the gulf of St. Lawrence the tidal amplitude 

 is very slight and amounts at most to only four and one-half feet. 

 There is very little mixing of the water, which as a result exhibits 

 during the summer a rather thick surface stratum of low salinity and 



