in various Latitudes of the European Seas. 117 



The size attained by Haliotis tuherculata in Guernsey is cer- 

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

 northern position, maybe 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 the Riiifficula of Vigo, it is questionable whether 

 it is the same species as R. flMncw/fl/rt of the Mediterranean, as, in 

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

 of stria?, with which the other is furnished; and Mr. \Voodward 

 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 Mnctra 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 j\lgarve and Cadiz ; one or two stray valves m. 

 the ^Mediterranean, and the same at ^logador. 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 Tcelandicus attains its largest dimensions on the coast of 

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

 bcrgen. Margarita alahastrum (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 soiith as Gibraltar 

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

 which accounts for the extent of its range southward. 



Trochus cinerurius and T. tumidus have their greatest develop- 

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

 are found progressively and uniforndy smaller as we proceed 

 southward. Trochus lineatus, which 1 have never encountered 

 north of the British Isles, attains its largest dimensions in 

 the neighbourhood of Vigo. 



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

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

 traced from Fininark to its southern termination in the British 

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



