COOKE : ON GEOGRAPHICAL DISTRIBUTION. 103 



Australia and New Zealand. Kraiiss' enumerates no less than 

 twenty-one species of Cape Patella, which more modern investigation 

 onlv reduces to seventeen. Patella proper occurs almost all over the 

 world, but is not characteristic of the cold boreal or Antarctic waters. 

 In the latter, as well as in the Califoruian region, it is largely replaced 

 by the Nacella group, while in North Europe and the north-east coast 

 of Asia it becomes rare in species. Our own Patella vulgata, L., 

 finds its northern limit in the Faroe and Lofoden Islands ; it does 

 not occur in Iceland or in Greenland, and thus took no part in the 

 spread of those littoral ]\rollusca which are conveniently described as 

 ' circunipolar '. The Helcioniscuft group of Patella spreads all over 

 the Eastern Hemisphere and touches the Western at Chili, Juan 

 Eernaudez, and the Sandwich Islands, but is absent from West 

 Africa, yvheve Patella proper is strongly represented. On the western 

 shores of North and South America Patella is replaced by Acmcea, 

 except within the Tropics, where a few species of true Patella occur, 

 amongst them the giant P. mexicana, Brod., ranging from Mazatlan 

 and Acapulco to Paita, and occasionally measuring 14 inches in length. 

 The fact is significant that Aoncea is entirely absent from all African 

 waters, where Patella is so abundant, while it occurs liberally in 

 certain districts, i.e. Western North America, from which Patella 

 proper is absent. Yet it would not be safe to assume that the genera 

 are mutually exclusive, or that shores not occupied by the one 

 genus have been appropriated by the other. Further study of their 

 distribution would probably throw light on these points. The scarcity 

 of Patellidse on the coast of East America may perhaps be due to the 

 want of rocky surface to which they could attach themselves, the 

 coast being, in the main, low-lying and sandy. 



Ilaliotis is another genus, belonging in the main to shallow water, 

 whose distribution would repay further investigation. Certain facts 

 are plain : tliat Australia and the adjoining seas are the focus of its 

 distribution, and that there are two well-marked sub-foci in Japan 

 and North- West America. " Not one species- is found on the eastern 

 coast of North or South America, and only one {II. pourtalesii'^) on 

 the west coast of America south of Lower California." The northern 

 range of our own U. tulerculata is, as is well known, the Channel 

 Islands, 49° N. hit. It would be interesting to know exactly how far 

 north H. laniscliathana, Jonas, extends on the coasts of British 

 Columbia and Kamschatka. Nothing definite seems to be known 

 of the range of the South African species on the east and west coasts 

 of that continent. 



The distribution of Purpura, a very marked littoral genus, would 

 amply repay careful study. Especially one would like to know the 



^ Sildafrikanisclien Mollusken, pp. 43-57. 



" H. A. Pilsbry, Manual of Conchology, vol. xii, p. 73. 



■' Dredged in 33 f. sand, at Charles I., Galapagos. Pourtales dredged one living 

 Haliotis (the specimen has since been lost) from the bed of the Gulf 

 Stream, in 200 f., near Florida reefs. No specimens of Haliotis have 

 since been found in the West Atlantic or Gulf of Mexico. 



