S6 THE BLUE CRAB PIERS. 



only measure 4.65 inches and 5.90 inches, and the males are all 

 6.03 inches or less in breadth, we are lead to the conclusion that 

 our Nova Scotian individuals undergo their final moult and so 

 attain maturity at a smaller size then do those of the more 

 favourable southern coast. This is as might be expected on 

 the extreme northern extension of the geographical range, where 

 suitable food may not be so abundant, and the torpid winter 

 condition may be slightly longer, as this crab becomes sluggish 

 when the temperature of the water falls below 50 degrees. 



Conclusion.— We thus see that at this northern locality on the 

 Atlantic coast of Nova Scotia, in latitude 44° 37', there is a re- 

 markable and apparently well-established and comparatively 

 numerous colony of this important species of crab, which pre- 

 viously had never been recorded from Canadian waters, or even 

 from further north than Salem Harbour, Mass., situated in 

 latitude 42° 30', nearly four hundred miles to the southwest. 

 It seems truly remarkable that this crab has not been found in 

 the Bay of Fundy, except the single specimen from Sandford, 

 Yarmouth Co., or even on the coast of Maine.* It would be 

 interesting to know if it occurs in suitable localities elsewhere 

 along our Nova Scotian Atlantic coast, or whether at Cow Bay 

 and Sandford, we have isolated colonies whose origin may have 

 been casual individuals, or even a single egg-bearing female, 

 borne northeastward on the Gulf Stream and thence straying 

 to our shore. This current has brought many unexpected 

 marine visitors from the south. Such accidental crustacean 

 wanderers, if cast upon a favourable part of the coast, where 

 suitable food occurred, could multiply and establish themselves. 

 The marked swimming ability of the family to which the Blue 

 Crab belongs, may lend strength to such an explanation of the 

 origin of such colonies here, should subsequent observations 

 indicate that the species does not occur in the intervening area 

 between Nova Scotia and Massachussetts.f Nothing at present 

 indicates that the Cow Bay colony and the Sandford individual 

 are the survivors of an occupation which once extended un- 

 broken up to this latitude. 



* See Rathbun's List of Crustacea of New England, 1905. 



1 W. P. Hay (Life History of Blue Crab. Rept. U. S. Bur. of Fisheries. 1904. p. 401. Wash., 

 1905) says the species is one of great activity and considerable power of endurance. It pro- 

 gresses through the water by a sculling motion of the broad hind less, and under ordinary 

 conditions it moves slowly, its efforts apparently being to keep afloat while it is borne along by 

 the current. In this way it might easily go adrift and be carried northward by the set of the 

 Gulf Stream. 



