56 



THE ROYAL SOCIETY OF CANADA 



high temperature. The deep water has a temperature in the neigh- 

 bourhood of zero on the Centigrade scale, and frequently below that 

 point. A low water datum used by Dr. Dawson in his tidal survey 

 of 1915 was available as a level to which to refer the distributional 

 data that we obtained at that point. Dr. Dawson, to whom our 

 sincere thanks are due, has been so kind as to provide us for this 

 locality also with calculations as to the percentage of the total time 

 that various intertidal levels are covered and uncovered by water. 

 These have been made in the same manner as were those for St. 

 Andrews, and we give them below. 



Cheticamp or Eastern Harbour, N.S. 



Periods, Julv 18 to Aug. 16; 

 Oct. 14 to Nov. 12, 1915. 



Height above 

 datum 



low-water 



Months . 



Total number of hours cov 

 ered or uncovered 



Mean monthly total ir 

 hours 



Mean monthly percentage 

 of total time 



Uncovered. 



ft. 



1 ft. 



July 



44:50 



Oct. 

 29:20 



37:05 

 5-23 



2 ft. 



July 



305:30 



245:40 

 I 34-65 



Oct 

 185:50 



Covered. 



3 ft. 



July 



98:40 



Oct. 

 175:00 



136:40 

 19-30 



4 ft. 



July 



Oct. 



19:15 

 2-71 



Although the monthly differences here are great, the slightness 

 of the amplitude makes this of little moment, and the figure that we 

 have drawn with the mean monthly percentages as a basis is a fair 

 approximation to the average condition. The figure (2) has been 

 drawn in a similar manner to that for St. Andrews {vide supra) and 

 the sides of the part representing the intertidal conditions are far 

 from straight, for they form sigmoid curves. 



The periwinkle occurs between tides to a height of over four 

 feet above low water datum and also goes far below, down to a depth 

 of nearly twenty fathoms. The barnacle reaches a height of about 

 three and one half feet and is also to be found below low-water mark, 

 but we did not determine its lower limit of distribution. The same 

 is true of the mussel, which reached a level of nearly two feet above 

 the low water datum. In the Woods Holl region it occurs abundantly 

 at depths as great as nineteen fathoms and the probability is that at 

 Cheticamp it has a similar distribution. 



Although small sea-urchins were occasionally taken at slight 

 depths, the large individuals such as we found between tides at St. 

 Andrews, were met with only at depths of twenty-four fathoms or 

 more, and down to fifty fathoms which was the greatest depth to be 

 found. The whelk occurred only at depths of from twenty- five to 

 thirty-five fathoms. As it is without a pelagic stage in its life history 



