178 PERCY SLADEN TRUST EXPEDITION. 
animal life. Green weed, too, of every sort is practically absent. However, this 
barrenness is amply compensated for by the enormous quantity of Nullipores (Litho- 
thamnia, &c.), incrusting, massive, mammillated, columnar, and branching. The 
outgrowing seaward edges of the reefs are practically formed by their growths, and it is 
not too much to say that, were it not for the abundance and large masses of these 
organisms, there would be no atolls with surface reefs in the Chagos. The lagoon shoals 
of Egmont are covered by them, and are the only lagoon reefs in the Chagos that reach 
the surface; having once done so, they die and become hollowed out, finally resembling 
miniature atolls.” Concerning Salomon, which was carefully surveyed, he remarks that 
‘its face was everywhere singularly barren ; Lithothamnion, Polytrema, and, of course, 
reef-corals were not obtained below 50 fathoms.” Further, he observes in another paper * 
as to the Chagos :—‘ Individually the reefs present the same general characters as 
those of the Maldives. They differ, however, in detail in that their outgrowing edges 
are, practically entirely, formed of Nullipores, though corals are important builders from 
5 to 30 fathoms.” (Cp. the photo J. ¢. p. 331, from He de la Passe, Salomon Atoll, 
showing Nullipore buttress growing out from the seaward edge of the reef.) 
The species of calcareous alge of the group in question occurring so numerously in 
the Chagos are Lithophyllum onkodes, L. eraspedium, L. Gardineri, and Goniolithon 
Jrutescens. These species thus are important reef-builders, especially the two or three 
first-mentioned ones, comprising the incrusting, massive, mammillated, and columnar 
forms, whereas the species last mentioned is a more delicate branching species. It is 
possible that, besides the species mentioned, other species are also to be found, which the 
collector may have failed to notice. If so, they are certainly playing no prominent part 
in the formation of reefs. 
At Diego Garcia three species have been collected by the German ‘ Valdivia’ Expedition t, 
viz. :—small specimens of Lithoph. onkodes attached to corals, a specimen of the small 
crust-like Lithothamnion simulans (earlier only known from the Gulf of Siam), and a young 
specimen of Lithophyllum Kaiseri (pallescens) mentioned below. 
CARGADOS CARAJOS. 
Near Cargados is, according to the Report (/. ¢. p. 5), “a wonderfully constant depth 
of 30-85 fathoms over the body of the bank .... the bottom was either coral rubble, 
white sand, shell rubble, or weed. The three latter occurred only in the central parts of 
the bank.... From this rubble, which is of a bright red colour, due to an encrusting 
nullipore, we obtained a rich variety of animal life, nearly all forms tinted with red.” 
In this bank, where more than 30 hauls were made, Lithothamnion indicum occurred 
in four localities (No. B 8, B9, B18, and B14), and in two of the same localities (No. B& 
and B14) also Lithothamnion australe, both together with a number of young, stunted 
or dead and undeterminable specimens not unlikely belonging to the first-named species. 
* J. Stanley Gardiner, “ The Indian Ocean,” The Geographical Journal, October and November, 1906, p. 323. 
+ The species coliected by this expedition at Diego Garcia and Mahé will be mentioned by Mr. Th. Reinbold in 
Wissenschaftliche Ergebnisse der Deutschen Tiefsee-Expedition.’ 
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