PLANT AND ANIMAL ASSOCIATIONS 55 



The periwinkle, L. Itttorea, appeared for the first time 

 on the coast of Canada at Bathurst, New Brunswick, in 

 1855, and spread thence by stages southwards. It was 

 recorded from the Nova Scotian coast in 1868, then 

 from Maine, and so onward as far as New Haven and 

 Newport (Rhode Island) by 1880. It is believed to have 

 been transported in the first instance in ballast. Further 

 south than New Haven the animal has encountered its tem- 

 perature limit, namely, water of 26° C, a temperature fatal 

 to its floating masses of ova. Its southern limit on the 

 coasts of the Old World is the Gulf of Gascony (Pelseneer, 

 1914). The struggle for foothold is well exhibited by the 

 common Cirriped Balamis halanoides, which colonises even 

 the most wave-swept rocks and boulders. During the 

 recent observations in the Port Erin district, already men- 

 tioned (Mayne, 19 18), this species was found to be most 

 abundant on rocks between three-quarters and full-tide 

 levels, growing thickly on the big boulders and flat-topped 

 rocks : in all cases on the metamorphic " Manx Slates." 

 On the hmestone shore at Port St. Mary patches of small 

 ones were found, but sparsely scattered between compara- 

 tively large areas of the alga Enter otnorpha, and the two 

 never seemed to inhabit the same piece of rock. In this 

 connection Orton (19 15) records a case at Plymouth in which 

 specimens of Patella (the common limpet) had eaten out 

 paths in the green algae (chiefly young Enteromorpha) on 

 cement piles between tide-marks. These paths radiated 

 from the " scar " of the limpet, and showed fine lines made 

 by the teeth of the radula : Balamis spat settled along these 

 cleared spaces. 



Miss Mayne carried out some enumerations of Balamis, 

 using a wooden frame one foot square, which was laid upon 

 the rock, and all within counted by hundreds, and ticked 

 oflF with a blue pencil to avoid errors. In one case 2940 

 occurred within a square foot, varying in size from ~ inch 

 to f inch across the base ; while of another lot (in 

 another place) 11 38 were counted within a square foot, the 

 average size being | inch. Petersen and Jensen (191 1) 



