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



by Risso and subsequent authors. There are two principal 

 zones, the littoral and the submarine ; the nature of habitat 

 and supply of food influence the residence and migration of 

 animals, not the depth of water. Psammohia costulata and 

 Buccinum undatum are instances in support of this proposi- 

 tion." 



Now a natural inference from this would be that, excepting 

 those which are littoral, the species inhabit all depths indif- 

 ferently, which I know it could never have been Mr. JefFreys's 

 intention to imply. Admitting that ^' the nature of the habitat 

 and supply of food influence the residence of animals," it is 

 evident that these must vary to meet the requirements of dif- 

 ferent species, also that depth is not only itself an important 

 element in the nature of a habitat, but must have considerable 

 influence on the food of Mollusca. For instance, the Lami- 

 nar ia does not grow below 15 or 20 fathoms at the most ; 

 several species of Mollusca are entirely dependent upon Lami- 

 naria for food, and consequently are strictly confined to its 

 zone. In most cases the conditions cannot be so easily de- 

 fined ; but it is nevertheless a fact that most, if not all, the 

 species of Mollusca have their maximum of development at a 

 particular depth — and that while some enjoy a considerable 

 bathymetrical range, others are confined within comparatively 

 narrow limits — and that, in consequence of the great interest 

 attached to vertical distribution, it has been found convenient 

 to institute zones of depth as well as geographical provinces. 



According to Forbes, there exist in the eastern Mediterra- 

 nean eight well-marked regions of depth, each characterized 

 by its peculiar fauna. K^ this conclusion was arrived at after 

 some eighteen months of research by no ordinary observer, I 

 consider that it is entitled to respect until the data upon which 

 it is founded, set forth in the Report on the ^gean Inverte- 

 brata, shall have been proved to be erroneous. It does not fol- 

 low that observations made in the ^gean Sea are of universal 

 application, or that different conditions in the ocean or other 

 seas may not require a modification in the number or extent 

 of the zones. Where the action of the tide is considerable, 

 there are, in fact, an upper and a lower littoral zone — some 

 species of Mollusca as well as of marine plants being found 

 even beyond the reach of ordinary tides, while others are not 

 to be met with much above the lowest water-mark. It is to 

 be noted that the same species often frequent difl'erent depths 

 in different seas ; and in these cases it is generally where the 

 climate and other conditions are most favourable to their exis- 

 tence and multiplication that they inhabit the shallowest 

 water. Several of the rare Shetland species, which might 



