268 
THE VOYAGE OF H.M.S. CHALLENGER. 
the name Rhabdammina irregularis. 1 I am informed by the Rev. A. M. Norman that a 
variety with branching arms was also obtained in the dredging operations of “ le 
Travailleur” in the Bay of Biscay, in 1880. 
The walls of the test are composed chiefly of coarse sand, the grains of which are of 
various sizes, and taken apparently without much selection (figs. 12, 13). The nature of 
the mortar employed for incorporating the siliceous material cannot be positively stated, 
but chemical analysis reveals the fact that, next to silica, peroxide of iron is the largest 
constituent of the test, and in the absence of any considerable proportion of carbonate of 
lime, it is fair to conclude that the cement is, to a greater or less extent, a ferruginous 
compound. Be this as it may, the resulting wall is hard and compact, and forms as strong 
and effective a protection as a thick homogeneous shell. The test is invariably coloured, 
but the precise tint differs in different localities. In the North Atlantic it takes various 
light shades of reddish-brown, whilst at certain points in the East Indian seas it is of much 
darker hue, sometimes almost black; the difference in fact between fig. 13 and fig. 12. 
The colouring matter appears to be in part organic. 
The area of the geographical distribution of Rhabdammina abyssorum is almost 
world-wide. The most northerly points are the shores of Franz- Josef Land, about lat. 
80° N., 108 fathoms, and Barents Sea, 219 fathoms. Of its presence in the Arctic 
Ocean, Prof. G. 0. Sars states in a letter to the author, that in the region lying 
east of Finmark, Bear Island, and Spitzbergen, the typical stellate form exists in such 
abundance as to render the term Rhabdammina ooze not inappropriate for the dredged 
mud. It is found on the coast of Norway, 450 fathoms (M. Sars) ; in the Hardanger 
Fiord, 500 fathoms (G. O. Sars) ; in the Gulf of St. Lawrence, 220 fathoms (Whiteaves) ; 
in deep water in the Bay of Biscay (Norman) ; in the warm area of the Faroe Channel, 
305 to 542 fathoms ; south of the Rockall Bank, 630 fathoms ; south-west of Ireland, 862 
fathoms and 2435 fathoms; off the Canaries, 1125 fathoms; and at two Stations near 
the Azores, 900 fathoms and 1000 fathoms. In the South Atlantic it has only been 
noticed at one Station, east of Buenos Ayres, 1900 fathoms. Its southern limit, so far as 
our present knowledge extends, is Station 146, lat 46° 46' S., between the Cape 
of Good Hope and the Kerguelen Islands, 1375 fathoms. In the South Pacific it occurs 
off Sydney, 410 fathoms; off Amboyna, 1425 fathoms; and off the north coast of 
Papua, just under the equator, where it is exceedingly abundant, 1070 fathoms. 
Rhabdammina discreta. H. B. Brady (PI. XXII. figs. 7-10). 
Rhabdopleura, sp., G. M. Dawson, 1870, Canad. Nat., vol. v. N. S., p. 176, woodcut, fig. 7. 
Rhabdammina discreta , Brady, 1881, Quart. Journ. Micr. Sci., vol. xxi. N. S., p. 48. 
Test cylindrical, open at both ends ; consisting of a straight or nearly straight tube 
of indefinite length, spuriously segmented by slight constrictions at irregular intervals. 
1 Proc. Roy. Soc., 1869, vol. xviii. p. 60. 
