1 



PACTS AND OBSERVATIONS. 



This Table gives the results of 5000 acts of dredging (minus two), as performed by experienced 

 naturalists in eleven large districts, in eleven sea-bottoms. Edward Forbes, M 'Andrew, and Gwyn 

 Jeffreys conducted these operations as their only object, as also did Cuming ; but both Cuming and 

 Hinds passed rapidly over large spaces of sea in irregular pursuit of the animals only, and not as 

 investigators of any district. Adams evidently moved over littoral and other small depths, for he 

 was often among rocks and stones. Forbes laboured in laminarian and medium depths; for 

 gravel, shingle, sand, and weeds figure largely in his lists, while there is little mention of rock, and 

 none of white mud. Hinds worked a good deal over the same level, but rested nowhere, so that 

 most of his species are constant to two, often intermixed, grounds. Perhaps Forbes, M f Andrew, 

 and Cuming swept over the largest extent of sea. 



Every one of these eleven districts carries with it its own interpretation, and deserves an indepen- 

 dent study. Some were nearly closed basins ; others ran down latitudes along shores oftenstraight ; 

 others, again, consisted of open sea. They presented many other differences, local and climatal. 



T^Jie object of this Table (Z) is to show, to measure, the extent of modern divergence in 3137 

 species of marine life taken in the mass, throwing aside for a moment any .further artificial 

 arrangement. 



Taking the sums total of the grounds, it points out the comparative faunal occupancy of each 

 over large regions. Rock presents 313 appearances, for instance, one sixteenth of the whole 

 appearances ; stones and gravel a tenth ; shingle one twentieth ; sand considerably above a quarter. 

 By inference it tells the extent and importance to living creatures of these grounds, their depths, 

 and other particulars. 



The total number of appearances in this Table (as already defined) is 4987, being 1849 above 

 the actual species, an excess spread irregularly over all the grounds. The species constant to one 

 ground are 1145; to what particular grounds especially, I do not know. The divergent species 

 (1993) are nearly double this number a fact of great importance, as assisting in the act of migra- 

 tion, our main concern here. 



The constant and divergent mollusks vary in number with the kind of sea they inhabit. In 

 the open sea the former are few and the latter are numerous ; in close waters this is reversed. Thus 

 we see in Vigo and Carthagena bays, and perhaps on the British coasts, the constants are many, 

 and wanderers are seldom seen. In support of this statement we find that in the above-named 

 bays, of 141 Gasteropoda, 94 are constants; and of 117 Acephala, 100 are constants. These two 

 orders represent the bulk of the animal life of the localities. Here M f Andrew worked assiduously 

 for fourteen weeks. 



Brown mud (argillaceous) with some siliceous sand, or a little lime, is the seat of one-third of 

 the marine population of Table Z ; and quartzose sand, more or less pure, contains a still larger fauna. 

 Stones and gravel are well frequented ; rock, weed, and nullipore much less so (in these lists), and 

 about equally. White mud is barely mentioned by five of the dredgers. 



As the following Table (2 A) occupies very little space, and brings to view many noteworthy 

 particulars, I venture to insert it. 



TABLE 2 A. Molluscan Orders. 



