52 PERCY SLADEN TRUST EXPEDITION. 
flat surface exposed for nearly a foot at low spring-tides. A second near it was similar, 
about 100 yards across, and slightly hollowed out in the centre, where all the organic 
growth was dead. Otherwise both were completely covered with every conceivable 
branching or columnar form of Lithothamnia, every plant being of precisely the same 
brilliant red-pink colour (Pl. 9). No other important building-agents were found on 
the surface or slopes of either. Another shoal visited on the same day, to some degree 
enclosed in the north-west end of the atoll, was similar to the second, being a little dead 
in the centre, but its surface was formed by dull orange encrusting Lithothamnia. It 
was obviously, however, a mere skin, its real builders being corals, of which we noted 
six genera, together with Millepora and Tubipora, growing on its edges. The three 
shoals examined overhung their bases to some slight degree, but there was no sign of 
any falling. All seemed so completely covered with organisms, save in their centres, that 
Fig. 23. 
Shoals in the lagoon of Egmont Atoll at low tide. 
decay did not seem possible. They forced themselves on our notice, since they would be 
taken to represent, according to one theory, the first stage of miniature atolls, arising, 
in this case, within a true atoll, the lagoon of which, quite contrary to the same theory, 
they would be materially aiding to fill up. 
The presence of these Lithothamnia shoals would naturally be taken as evidence of 
oceanic characters in the lagoon, in particular in its having continual change in its water, 
little being stationary. Theoretically this should mean that a greater variety of animal 
life ought to be found than in a more enclosed lagoon. Actually the contrary was the 
case. The total quantity of sedentary organisms (corals and Lithothamnia) was no doubt 
greater, but free-living animals were decidedly scarce. The dredgings did not bring up 
a tithe of what was obtained at Diego Garcia, and reef-collecting was a failure, though 
we secured some Chitons, Haliotis, and Nudibranchs which we had not seen before. 
The reason would seem partly to be the absence of nooks and crevices in which animals 
