COOKE : ON GEOGRAPHICAL DISTRIBUTION. 109 



still further south.' Has anyone observed that the surface temperature 

 of the water on our north-eastern coast has fallen, during the last fifty 

 years? Cassidaria tyrrhena, L., which was first added to the British 

 fauna in 1870, and subsequently dredged o£E the Kerry coast and off 

 the Scillies, has of late been trawled in considerable numbers in the 

 deep trough between Miltbrd Haven and the Irish coast, off the 

 Saltees lightship, and appears to be moving northward. 



In the list of the Mollusca of Long IslaiuP published by Sanderson 

 Smith and Temple Prime in 1870, a list which embodied the results 

 of eleven years' collecting, Littorina littorea, L., did not occur. F. N. 

 Balch, publishing^ in 1899 a list of the marine Mollusca of Coldspring 

 Harbour, Long Island, remarks : " Ten years ago it might have been 

 possible to define a spot within 60 miles by saying it was a place 

 where Purpura lapillus was not, and Litt. littorea was, found, but 

 now the wave of the conquering European species has spread far down 

 toward Virginia, and at Coldspring the native competitor {Nassa 

 ohsoleta) begins to yield room." 



When the agency of man gives them a chance of extending their 

 area the Mollusca are as quick to take advantage of their opportunity 

 as the rabbit was in Australia. The spread of Mediterranean and 

 Eed Sea species into the waters of the Suez Canal has been commented 

 upon by Tillier and Bavay, by Faurot and others. T^o doubt our 

 American friends will be erjually ready to note the results of the 

 opening of the Panama Canal, and to observe whether the ' homo- 

 logous species ' which, in some numbers, inhabit the two sides of 

 Central America, show any signs of approximation, as a residt of the 

 mingling of waters which have been separated since the Miocene 

 epoch. 



We have watched the almost meteoric swiftness with which 

 Petricola pholadiformis, Lam., and Crepidula fornicata, Lam., have 

 established themselves in European waters. The former, after having 

 first been noticed in the Eiver Crouch, Essex, in 1890, wasat Shellness 

 and Heme Bay in 1896, in 1901 it had reached Belgium, and was 

 notified from Ostend in 1903 and Dunkirk in 1906, in 1907 it had 

 spread all over the Suffolk coast, Denmark notified it in 1906-7, in 

 1908 it was at Noordwijk, Holland, in 1910 at the mouth of the 

 Medway, and the same year at Shallinger, Denmark. It will be 

 interesting to see at what point short of the Baltic it stops. Of 

 C. fornicata, dead shells of which were first notified at Cleethorpes 

 in 1887, 10 tons of live specimens were dredged* in four weeks in 

 the Blackwater Biver twenty years later. 



Urosalpinx einerea, Say, has been transplanted with East American 

 oysters to the Pacific coast. A quart of specimens of this oyster 

 scourge has been collected in less than ten minutes at Belmont, near 

 San Francisco.^ 



' J. A. Hargreaves, Journ. Conch., vol. xiii, p. 89, 1910. 

 - Ann. Lye. Nat. Hist. N. York, vol. x, pp. 377-407, 1870. 

 5 Proc. Boston Soc. Nat. Hist. (7), vol. xxix, pp. 133-62, 1899. 

 ■* J. Murie, Zoologist, ser. IV, vol. xv, pp. 401-15, 1911. 

 ^ E. E. C. Stearns, Nautilus, vol. viii, p. 13, 1894. 



