REPORT ON THE RADIOLARIA. clv 



derived from the pure Eadiolarian ooze, which forms the bed of the Central Pacific at 

 depths of from 2000 to 4000 fathoms (§ 237). Many of these abyssal forms were brought 

 up with the malacoma uninjured, and they show, both when mounted immediately in 

 balsam, and when preserved in alcohol, all the soft parts almost as clearly as fresh prepara- 

 tions of pelagic Radiolaria. These species are to be regarded as truly abyssal, i.e., as forms 

 which live floating only a little distance above the bottom of the deep-sea, having become 

 adapted to the peculiar conditions of life which obtain in the lowest regions of the ocean. 

 Probably the majority of the Ph.eodaria belong to these abyssal Radiolaria, as well as a 

 large number of Nassellaria, but on the other hand, only a small number of Acantharia 

 and Spumellakia are found there. A character common to these abyssal forms, and 

 rarely found in those from the surface or from slight depths, is found in their small size 

 and their heavy massive skeletons, in which they strikingly resemble the fossil Radiolaria 

 of Barbados and the Nicobar Islands. The lattice-work of the shell is coarser, its 

 trabecule thicker and its pores smaller than in pelagic species of the same group ; also 

 the apophyses (spines, spathillaj, coronets, &c.), are much less developed than in the 

 latter. From these true abyssal Radiolaria must be carefully distinguished those species 

 whose empty skeletons, devoid of all soft parts, occur also in the Radiolarian ooze of the 

 deep-sea, but are clearly only the sunken remains of dead forms, which have lived at the 

 surface or in some of the upper zones; 



236. Deposits containing Radiolaria. — The richest collection of Radiolaria is found 

 in the deposits of ooze which form the bed of the ocean. Although the pelagic material 

 skimmed from the surface of the sea, and the zonarial material taken by sinking the tow- 

 net to various depths, are always more or less rich in Radiolaria, still the number of 

 species thus obtained, is, on the whole, much less than has hitherto been got merely from 

 deep-sea deposits. Of course the skeletons found in the mud of the ocean-bed, may 

 belong either to the abyssal species which live there (§ 235), or to the zonarial (§ 234), or 

 to the pelagic species (§ 233), for the siliceous skeletons of these latter sink to the bottom 

 after their death. Almost all these remains found in the deposits belong to the siliceous 

 " Polycystina " (Spumellaria and Nassellaria) ; Ph^odaria occur but sparingly, and 

 Acantharia are entirely wanting, for their acanthin skeleton readily dissolves. The 

 abundance of Radiolaria varies greatly according to the composition and origin of the 

 deposits. In general marine deposits may be divided into two main divisions, terrigenous 

 and abyssal, or, more shortly, muds and oozes. The terrigenous deposits (or muds) 

 include all those sediments which are made up for the most part of materials worn away 

 from the coasts of continents and islands, or brought down into the sea by rivers. Their 

 greatest extent from the coast is about 200 nautical miles. They contain varpng 

 quantities of Radiolaria, but much fewer than those of the next group. The abyssal 

 deposits (or oozes) usually commence at a distance of from 100 to 200 nautical miles 



