440 OCEANOGRAPHY, BIONOMICS, AND AQUICULTURE. 



or a sheltered corner in which the finer particles suspended in the water 

 are able to sink, or it may be due to the wearing - away of a limestone 

 beach, or to quantities of alluvium brought down by a stream from the 

 laud, or to the presence of a submerged bed of bowlder clay, or even, in 

 some places, to the sewage and refuse from coast towns. Finally, there 

 is the deep-water mud, a very stiff blue- gray substance which sets, 

 when dried, into a firm clay, and this is, I take it, the mud of which 

 Dr. Murray writes, liut in none of these cases, and certainly not in 

 the last mentioned, is there in my experience or in that of several other 

 naturalists I have consulted, auy rich fauna associated with the mud. 

 In fact, I would regard mud as supporting a comparatively poor fauna 

 as compared with other shallow- water deposits. 



For practical purposes, round our own British coasts, it is still con- 

 venient to make use of the zones of depth marked out by Forbes. The 

 first of these is the " Littoral zone," the space between tide marks, 

 characterized by the abundance of seaweeds, belonging to the genera 

 Lichina, Fucus, Enter omorpha, Polysiphonia, and others, and by large 

 numbers of individuals belonging to common species of Balanus, 

 Mytilus, Littorina, Purpura, and Patella amongst animals. The second 

 zone is the "Laminarian," which extends from low-water mark to a 

 depth of a few fathoms, characterized by the abundant growth of large 

 seaweeds, belonging to the genera Laminaria, Alaria, and JlimanthaUa, 

 and by the presence of the beautiful red seaweeds (Floridese). There 

 is abundance of vegetable food, and animals of all groups swarm in 

 this zone, the numbers both of species and of individuals being very 

 great. The genera Helcion, Trochus, and Lacuna are characteristic 

 molluscan forms in our seas. Next comes Forbes's " Coralline" zone, 

 badly so named, extending from about 10 to 40 or 50 fathoms or so. 

 Here we are beyond the range of the ordinary seaweeds, but the 

 calcareous, coral-like iSTullipores are present in places in such abun- 

 dance as to make up deposits covering the floor of the sea for miles. 

 Hydroid zoophytes and polyzoa are also abundant, and it is in this zone 

 that we find the shell beds lying off our coasts, produced by great 

 accumulations of species of Pecten, Ostrea, Pectuneulus, Eusus, and 

 Buccinum, and forming rich feeding grounds for many of our larger 

 fishes. All groups of marine animals are pretty well represented in 

 this zone, and Antedon, Ophiothrix, Ophioglypha, Ebalia, Inachus, and 

 Eurynome may be mentioned as characteristic genera. Lastly, there is 

 what may be appropriately called the zone of deep mud (although 

 Forbes did not call it so), extending from some 50 fathoms down to (in 

 our seas) 100 or so. The upper limit of this zone is Murray's mud-line. 

 We come upon it in the deep fjord-like sea lochs on the west of Scot- 

 land, and in the Irish Sea to the west of the Isle of Man. 



Now, of these four zones, my experience is that the last — that of 

 the deep mud — has by far the poorest fauna both in species and in 

 individuals. The mud has a peculiar fauna and one of great interest 



