152 MANUAL OF THE MOLLUSCA. 
3. Coralline zone.—In northern seas the belt of sea-weed that 
fringes the coast is succeeded by a zone where horny zoophytes 
abound, and the chief vegetable growth consists of Nullipore, 
which covers rocks and shells with its stony-looking incrusta- 
tions. This zone extends from 15 or 25, to 35 or 50 fathoms, 
and is inhabited by many of the predacious genera—Buccinum, 
Lfusus, Pleurotoma, Natica, Aporrhais, Philine, Velutina ; and by 
vegetable feeders, such as Fissurella, Emarginula, Pileopsis, 
Hulima, and Chemnitzia. The great banks of scallops belong 
to the shallower part of this region, and many bivalves of the 
genera Lima, Arca, Nucula, Astarte, Venus, Artemis, and Corbula. 
4, Deep-sea Coral-zone.—F rom 50 to 100 fathoms the Nullipore 
still abounds, and small branching corals to which the Tere- 
bratula adhere. In northern seas the largest corals (Oculina 
and Primnoa) are found in this zone, and shells are relatively 
more abundant, owing to the uniformity of temperature at these 
depths. These deep-water shells are mostly small and destitute 
of bright colours; but interesting from the circumstances under 
which they are found, their wide range, and high antiquity. 
Amongst the characteristic genera are Crania, Thetis, Necera, 
Cryptodon, Yoldia, Dentaliwm, and Scissurella. In the mud 
brought up from deep water may be often found the shells of 
Pteropoda, and other mollusca which live at the surface of the 
sea. In the Aigean Sea there is deep-water within one or two 
miles of the coast; but in the British Channel the depth seldom 
amounts to more than 20—40 fathoms. 
When registering the results of dredging operations, it is 
important to distinguish between dead and living shells, as in the 
preceding Tables; for almost every species is met with, in the 
condition of dead shells, at depths far greater than those in which © 
it actually lives. On precipitous coasts the littoral shells fall 
into deep water, and are mingled with the inhabitants of other 
zones; currents also may transport dead shells to some distance 
over the bed of the sea. But the principal agents by which so 
many decayed and broken shells are scattered over the bed 
of the deep-sea, must be the mollusk-eating fishes. Of 270 
species of boreal shells described by Dr. Gould (p. 60) more 
than half were obtained from the maws of fishes, in Boston 
market. Cod-fish do not swallow the large whelk-shells, but 
some idea of the number they consume may be derived from 
the fact that Mr. Warington has obtained the muscular foot 
and operculum of above 100 whelks, of large size, besides 
quantities of crustacea, from the maws of three cod-fish procured 
in the London market. Bivalve shells, like the Solens, and the 
