On Marine Dredging. 357 



that by a parallel law the northern marine fauna would be found in* 

 habiting great depths in the more southern seas ; indeed the observa- 

 tions of my friend Professor E. Forbes, published in his report upon 

 the invertebrataoftho Kgccan sea, are, by him, considered sufficient 

 to establish the fact. It may appear presumptuous in me to differ' 

 from so high an authority — one who is probably, in every respect, 

 better qualified than any naturalist of the day to form a decisive 

 opinion upon the subject — more especially (and I gladly take the 

 opportunity to acknowledge it), as it is entirely in consequence of his 

 instruction, and guided by his recommendations, that I have been 

 enabled, while following a pursuit undertaken originally for recrea- 

 tion, to render any service to the cause of science. True it is, 

 nevertheless, that my experience does not tend to confirm the above 

 hypothesis ; as I find various species common to the Mediterranean 

 and northern seas inhabiting as great or greater depths in the latter. 

 Also, the analogy does not appear to me to hold good, on account of 

 the great diminution of temperature which takes place on ascending 

 to high elevations in the atmosphere, and the comparatively even 

 temperature of the water at various depths. I am rather inclined 

 to the belief, that each species is best adapted to certain conditions 

 of climate and depth in which it attains its greatest development ; and 

 that the further it is found from its most favourable habitat, either 

 towards the north or south, it will be at a greater depth in order to 

 be removed from the influence of unfavourable climate. 1 would not 

 at present feel justified in asserting, with any confidence, that such 

 is the case ; and if it be, there are certainly many exceptions in lit- 

 toral or sublittoral species, which continue to be such wherever they 

 are to be met with, under all circumstances of climate. 



Touching the geographical range of the species of mollusca, in 

 order to arrive at a complete knowledge of the subject, it would be 

 necessary to compare together the fauna of every country and region, 

 which is not at present practicable for want of the necessary data, as 

 we possess lists of the mollusca of but ^qvi districts, and these more 

 or less imperfect. As far as is possible, with such information as 

 can be procured, it has been done by Dr Philippi, in his valuable 

 work upon the mollusca of the two Sicilies. 



It only comes within the scope of my present communication to 

 remark upon the distribution of the lower animals within the limited 

 area of our seas ; and from a desire not to trespass upon the time 

 and patience of the Society, by a dry enumeration of all the species, 

 with their various localities, 1 will confine myself to the statement 

 of such facts as I conceive most important ; even so I feel called 

 upon to entreat your indulgence, as it will be necessary to mention 

 not a few species, the names of which will be particularly uninterest- 

 ing to those who have never bestowed attention upon this branch of 

 natural history. 



The fauna of the British seas belongs to a division which has 



VOL. XLVI. NO. XCII. — APRIL 1849. 2 A 



