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tucles, either with the same or representative species ; and it 

 has been inferred, that by a parallel law the northern marine 

 fauna would be found inhabiting great depths in the more 

 southern seas ; indeed the observations of my friend Professor 

 E. Forbes, pubbshed in his report upon the invertebrata of 

 the Egsean 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 deci- 

 sive 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 recommen- 

 dations, that I have been enabled, while following a pursuit 

 undertaken originally for recreation, to render any service to 

 the cause of science. True, it is, nevertheless, that my expe- 

 rience 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 ascend- 

 ing to high elevations in the atmosphere, and the compara- 

 tively 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. I 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 

 littoral 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 molusca, 

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



M 



