in various Latitudes of the European Seas. 117 



The size attained by Haliotis tuberculata in Guernsey is cer- 

 tainly remarkable ; but that it is not owing entirely, if at all, to 

 northern position, may be inferred from the fact that it does not 

 vary in dimensions progressively with the latitude. When in- 

 habiting the coasts of the Bay of Biscay, it is no larger than in 

 the neighbourhood of Gibraltar. 



With respect to iheRingicula of Vigo, it is questionable whether 

 it is the same species as R. auriculata of the Mediterranean, as, in 

 addition to its extra size and solidity, it differs in being destitute 

 of striae, with which the other is furnished ; and Mr. Woodward 

 has suggested the possibility of its identity with a fossil species. 

 If it should prove to be R. auriculata, the same observation will 

 apply to it as to the Haliotis, that the increase in size is not 

 progressive. 



Touching Mactra rugosa, we require more information with 

 regard to its distribution. In Vigo Bay, dead shells, certainly 

 of large dimensions, are not unfrequent; but, after diligent 

 search, I could never succeed in obtaining a recent specimen 

 there. The other localities from which I have procured the spe- 

 cies are Faro in Algarve and Cadiz ; one or two stray valves in 

 the Mediterranean, and the same at Mogador. In Faro, where 

 the specimens found on the shore are much more recent than in 

 Vigo, they are nearly, if not quite, as large ; while at Cadiz, only 

 thirty miles further south, they are smallest. 



The Arctic species belonging to the genera Trichotropis, Tro- 

 phon, Margarita, and Admete, with some others, when they 

 extend into the Boreal and Celtic regions, are diminutive. Pec- 

 ten Icelandicus attains its largest dimensions on the coast of 

 Finmark, and is of very diminished size and solidity from Spitz- 

 bergen. Margarita alabasti^um (Boreal) does not appear to vary 

 in size from the North Cape to the seas of Zetland. Area rari- 

 dentata is generally distributed on the northern coasts of Nor- 

 way, where it is very much larger than in the Hebrides ; and a 

 few specimens which I have obtained as far south as Gibraltar 

 are still more minute. This species inhabits only deep water, 

 which accounts for the extent of its range southward. 



Trochus cinerai'ius and T. tumidus have their greatest develop- 

 ment in number and size on the northern coasts of Norway, and 

 are found progressively and uniformly smaller as we proceed 

 southward. Trochus lineatus, which I have never encountered 

 north of the British Isles, attains its largest dimensions in 

 the neighbourhood of Vigo. 



Astarte arctica is as large at Tromsoe, near the southern limit 

 of its range, as in higher latitudes. A. elliptica diminishes when 

 traced from Finmark to its southern termination in the British 

 seas. A. sulcata attains its maximum on our own coasts, dimi- 



