152 MANUAL or THE MOILUSCA. 



o. Coralline zone. — In northern seas the belt of sea-weed thafc 

 fringes the coast is succeeded by a zone TV'here 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, 

 Fiisus, Pleurofoma, Natica, Aporrhais, Fhiline, Velutina ; and by 

 vegetable feeders, such as Fissurella, Emarginula, Pileopsis, 

 Eulima, and Chemmtzia. The great banks of scallops belong 

 to the shallower part of this region, and many bivalves of the 

 genera Lima, Area, Nucula, Astarfe, Venus, Artemis, and Corhula. 



4. Deep-sea Coral-zone. — From 50 to 100 fathoms the Nullipore 

 still abounds, and small branching corals to which the Tere- 

 hratida adhere. In northern seas the largest corals {Ocidina 

 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, Dentaliiun, and Scissurella. In the mud 

 brought up from deep water may be often found the shells of 

 Pteropoda, and other moUusca which live at the surface of the 

 sea. In the -ZEgean 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 oj)erations, 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 jDrocured 

 in the London market. Bivalve shells, like the Solens, and the 



