REPORT ON THE FORAMINIFERA. 
IX 
two associated forms, though alike in other respects, presented one constant difference, 
namely, that the smaller shells had a large primordial chamber, whilst those of the 
larger variety had no recognisable primordial chamber, or one of very small size. The 
two forms were, however, in every case treated by de la Harpe as distinct species. 1 The 
more extended observations of M. Munier-Chalmas upon the genera Nummulites and 
Assilina 2 led to a somewhat different view, namely, that the difference was one of 
development only, and the “ pairs ” were two forms of the same species. The recent 
researches of the same author and of M. Schlumberger, upon other genera of Foraminifera, 
have revealed the existence of somewhat similar pairs amongst the Biloculine, Triloculine, 
Quinqueloculine, and Fabularian Miliolce . 3 
The last-named authors offer two hypotheses by which these facts may be explained, 
but reserve their conclusions for a future paper. It is nevertheless worth mentioning 
that, in a later memoir, Dr. de la Harpe, after noting the occurrence of Nummulites in 
couples, as already described, and indicating that a different spiral measurement 
accompanies the diminution or apparent absence of the primordial chamber, though 
expressing no definite opinion on the subject, suggests that he should have been inclined 
to regard the difference between the corresponding shells as one of sexual character, had 
it been clear that any distinction of sex existed amongst the Protozoa. 4 
Pelagic Species. — One of the subjects brought prominently into notice by the 
observations taken on the Challenger Expedition is the relation of the surface-fauna of 
the ocean to that of the bottom-deposits. So far as the Foraminifera are concerned 
the question is by no means a new one ; but the Challenger collections, and those more 
recently made by Mr. Murray on the cruises of the “Knight Errant” and “ Triton,” 
have brought many fresh facts into notice, and furnished new ground for its discussion. 
The Foraminifera as a rule are not of pelagic habit. On the contrary, by far the 
larger proportion, probably 98 or 99 per cent, of the known recent “species” or 
“ varieties,” including the whole of the porcellanous and arenaceous groups and the 
bulk of the hyaline forms, inhabit the sand or mud of the sea-bottom, and are endowed 
with no swimming or floating powers. This may be regarded as a well ascertained 
fact. But, on the other hand, there are a certain number of forms belonging to eight or 
perhaps nine genera, which it is equally certain pass their existence, either in part or 
entirely, at the surface of the ocean or in mid-water. The practical importance of these 
comparatively few species is due to the extraordinary "abundance in which they are found, 
and the relatively large proportion of the entire mass of the bottom-deposit which is made 
up of their shells. 
1 Bullet Soc. Vaudoise Sci. Nat., 1879, vol. xvi. pp. 229, 230. 
2 Bullet. Soc. cjdol. France, 1881, ser. 3, vol. viii. p. 300. 
3 Comptes r endue, 1883, vol. xcvi. pp. 862, 1598. 
4 Bullet. Soc. gdol. France , 1881, ser. 3, vol. ix. p. 171. 
(ZOOL. CHALL. EXP. — PART XXII. — 1884.) Y b 
