Mr. R. M^ Andrew on Mr. Jeffreys' s last Dredging Report. 359 



there be searched for in vain in less than about 80 fathoms, 

 are to be met with in much shallower water and greater fre- 

 quency on the coasts of northern Norway. 



Mr.Jeifreys's second proposition, that individuals and varie- 

 ties are generally of smaller size when found in deep water, is 

 confirmed by my own observation ; and I proceed to 



3. ^' The size of North-European specimens is usually 

 greater than that of South-European specimens of the same 

 species," — from which Imust record my dissent,more especially 

 if it is meant to be implied that size diminishes in proportion 

 to southern latitude. 



The examples he names in support of his hypothesis do not 

 bear it out, but might generally be quoted to prove (though 

 there are many exceptions) what I conceive to be the true 

 theory, viz. that species attain their largest dimensions under 

 those latitudes and conditions, though not in the particular 

 localities, most favourable to their numerical development ; 

 and it is quite consistent with this proposition that certain 

 species which find in high northern latitudes the circumstances 

 most favourable to their existence and increase [Saxicava arc- 

 tica^ Area raridentata^ and Chiton Hanleyi may be taken as 

 instances) should attain smaller growth in more southern 

 regions. 



Pecten septemradiatiis I have dredged on the Scandinavian 

 coast as far north as Finmark, without obtaining in its more 

 northern habitat a specimen so large as those of Loch Fyne, or 

 even larger than those of the Sicilian species (P. clavatus of 

 Poli) which Mr. Jeffreys assumes to be identical with it. 

 Pecten opercularis^ Astarte sulcata^ Artemis exoleta^ A. lincta^ 

 and Natica Alder i all appear to attain their greatest dimen- 

 sions in the British seas ; but they are all distributed from the 

 MediteiTanean or coasts of Spain to those of Nordland or 

 Finmark, and I have found them all as large in their more 

 southern as in their more northern habitat. My specimens of 

 Astarte sulcata from Gibraltar and from Finmark, the extremes 

 of its range, are of equal size, and, in fact, not distinguishable 

 one from the other. Lima Mans I have found largest at Oban ; 

 specimens from Nordland are similar to those from Loch Fyne. 

 Mytilus adriaticus is, as far as my observation goes, smaller 

 in more southern localities than in Britain ; and I am not 

 aware of its having been met with further north ; but in my 

 Dredging Report of 1856 I have given Britain as the locality 

 of its principal development. The same observations will 

 apply to Defrancia teres and Bulla utriculus as to Mytilus 

 adriaticus^ unless the former should prove to be identical with 

 Pleurotoma horeale of Loven. 



