Mr. E. M'Andrew on the Comparative Size of Mollusca. 315 



Mr. JeiFreys, choosing his own ground, and taking the British 

 Molhisca as a standard of comparison, names certain species 

 " in particular " as appearing to attain a larger size in our own 

 seas than in the south of Europe. I must say that he has not 

 been fortunate in the selection. Donax poUtus may possibly 

 acquire larger dimensions in Britain than in the jNlediterranean, 

 though, upon comparing my specimens, I find but little diffe- 

 rence between them. Rissoa stria tula is very rare : I have never 

 obtained an adult specimen in the south, and have no reason to 

 believe that it does not attain as large size in Cadiz as in Eng- 

 land. Avicula Turentina I have never myself obtained in the 

 British seas, and rarely in the Mediterranean. Forbes and 

 Hanley mention that the largest specimen they have seen mea- 

 sures nearly four inches in length ; my largest of very few spe- 

 cimens from Malaga measures barely three and a half inches. 

 Galeomma Turtoni is a rare species, of which I have taken but 

 very few specimens, principally in the north of Spain ; but it so 

 happens that the individual I have found furthest to the south 

 (in the Great Harbour of Syracuse) is larger than any I have 

 seen from the Channel Islands or elsewhere. Of Murex coral- 

 linus I have twice received specimens from the Channel Islands, 

 through the favour of ]Mr. Jeffreys ; but they are inferior in size 

 to the average of those from the Bay of Gibraltar. Trochus 

 striatus attains something like double the size in the !Mediterra- 

 nean that it does in the British seas ; and my specimens of 

 Lachesis mininia, both from the north of Spain and the Medi- 

 terranean, are about five times as large as the British — more than 

 double the length, and thick in proportion. Forbes and Ilanley 

 state the ordinary length to be one-fifth of an inch, which ex- 

 ceeds the size of my British specimens ; while the Spanish are 

 seven-sixteenths of an inch in length. 



It would be foreign to my object to argue in favour of the 

 geographical zones into which that part of the ocean which 

 washes the shores of Europe has been divided by naturalists ; 

 but it strikes me that he must be a bold man who would assert, 

 for instance, that the Arctic Sea has no existence in fact or in 

 nature, or that there are not species of Mollusca to which it 

 affords the natural habitat, and which degenerate or cease to 

 exist in wanner regions. The Temperate zone, occupying so 

 much greater range of latitude in our hemisphere than either 

 the Arctic or the Torrid zones, it has been found convenient to 

 divide upon the coasts of Europe into north-temperate or Boreal, 

 mid-temperate or Celtic, and south-tempcratc or Lusitanian ; 

 and I conceive it would not be difficult to show that each of 

 these affords the climate and conditions best adapted to peculiar 

 forms and species of Mollusca. 



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