250 REPORT—1850. 
rhais pes-carbonis, Poromya granulata, Tellina proxima, probably Terebra- 
tula cranium, and a few Echinoderms and Zoophytes. 
Certain species which enjoy a great vertical range in the north, extending 
through the second, third, and in part the fourth regions of depth, ure in the 
south found only within limited tracts of deep-sea, as— 
Cardium suecicum. Syndosmya intermedia. 
Nucula polii. Terebratula Caput-serpentis, 
Pecten fuci. Scalaria Trevelyana?. 
These species are essentially members of the boreal or glacial fauna, and 
their presence in the south is dependent, if my views be correct, on the 
former spread of the glacial sea, and the preservation of its inhabitants at the 
existing epoch in many isolated and distant localities, where they live usually 
at considerable depths in the midst cf, and mixed up with.an assemblage of 
creatures of a Celtic and often a much more southern character. 
How far the nature of the sea-bottom determines the number and diffusion of 
species.—In the preceding tables, the nature of the sea-bed is expressed by 
letters representing the several mineral characters of the bottom, whether 
sand, sandy mud, mud, rock, stones, gravel, muddy gravel, shelly, shell-sand, 
or nullipore; the last kind of bottom being that commonly called “coral” in 
the charts of the European seas. 
Now, though our evidence certainly goes to show that the range of species 
in depth and distance from shore is often considerably extended by a con- 
tinuity, whether vertical or horizontal, of the same kind of ground, yet as- 
suredly ground alone will not determine the extension of any species; for 
otherwise we should have the stone- and gravel-inhabiting species of the Lit- 
toral zone carried in many places into the Laminarian and Coralline zones, and 
the peculiar inhabitants of the muddy and sandy tracts in the Laminarian 
zone carried far into the depths of the sea, since in very many places these 
kinds of sea-bed range without interruption from shallows to great depths, 
But this is not the case ; no continuity of mud, for instance, enables Scrobz- 
cularia to live beyond its bounds, or the characteristic Rissoe of the gravelly 
parts of the Laminarian zone to extend themselves into the deep sea. 
The conditions of the sea-bottom which are most favourable to variety of 
species may best be illustrated by referring to those dredging papers in which 
the number of species of either univalve or bivalve testacea taken alive ex- 
ceeded ten. In the southernmost of the districts within the area under con- 
sideration, out of eighteen papers ten come under this category. Three of 
these belong to the Laminarian zone, five to the Coralline region, and two to 
the upper region of deep-sea corals. The three first-mentioned are all from 
a muddy and stony or gravelly bottom with weed, and within two miles of 
the shore ; their number of univalves exceeds that of bivalves ; in all three 
the number of living univalves is very high, being 15 and above; and in 
two of them the numbers of living bivalves are respectively 10 and 19, and of 
dead 9 and 1%. Of the five papers from the Coralline zone, four are within 
three miles from the shore; three of these are from bottoms more or less 
stony and gravelly, in one instance mingled with nullipore; and one is from 
a floor of shell sand. They are also very prolific; one in dead and living 
univalves, one in dead and living bivalves, and two equally so in bivalves 
and univalves. The fifth of these coralline papers is from a depth of 30 
fathoms and under, and a bottom of sand and gravel at a distance of 11 miles 
from shore; it exhibits a great preponderance of bivalves, and an equal 
number of species taken dead and alive. The two deep-sea papers are from 
a depth of 50 fathoms, on a sandy bottom, 60 miles from land ; they scarcely 
come under the head of prolific papers, since few living species were taken, 
To ae ~.. 
