862 Proceedings of the Royal Society 
Montipora , and Echinopora. Amongst the latter occur numerous 
Madreporce , such as M. liyacinthus (D.), M. effusa (D.), M. appressa 
(D.), and several other species. Pocilloporce , such as P. pulchella 
(Br.) and P. acuta ; (L.), here thrive ; also Seriatoporce (hystrix, D., 
and pacifica, Br.); Milleporce (intricata, E. & EL and gonagra , E. & 
H.), and Stylophora palmata (Bl.). The Eungidse are well repre- 
sented by several species of Fungia and Ctenactis , together with 
Halomitra tiara (V.), and a species of Podabacia not yet deter- 
mined. The massive corals here found are species of Porites 
usually possessing flat dead summits, and often 8 to 10 feet across ; 
species of Symphyllia , Goeloria , and Rhodorrhcea; and Pavia 
rotulosa (E. & S.). Amongst other of the common corals found in 
lagoons and lagoon-channels occur Heliopora coerulea * and Isopora 
labrosa (D.). The Heliopora prefers situations in the vicinity of 
openings in the reef, and all places where it can he exposed to a 
plentiful supply of sea-water. This hydroid coral, together with a 
massive species of Rhodorrhcea , with which it is associated, covers 
a considerable portion of the bottom of a small hoat-liarhour in 
Oima Atoll. Isopora labrosa often attaches itself to and partly 
invests Millepora gonagra (E. & H.). Alcyonarians also flourish 
in the quiet waters of the lagoon ; amongst them are species of 
Alcyonium , Xenia , and Anthelia. The Xenia, may occur in 
extensive beds encrusting and concealing the unsightly patches of 
the dead branching corals. A huge empty Tridacna shell, which 
was covered on the outer surfaces of its valves with this pretty 
Alcyonarian, formed quite a picture in Oima Atoll. Occasional 
masses of the Alcyonarian coral, Tubipora sp., are also to he observed. 
Amongst the algse that thrive in lagoons, is an edible species of 
Caiderpa , which is distinct from the non-edible species that grows 
on the reef-flat and in the wash of the surf ( vide p. 859). 
The observing naturalist will find abundant material for the 
study of the complex relations that exist between the multitudes of 
creatures that frequent coral reefs. The protective colouring of the 
small crabs that live among the branching corals often attracted my 
attention. I recall in particular the instance of a small crab that 
finds its home amongst the branches of a Pocillopora. The light 
purple colour of its carapace corresponds with the hue of the 
* Vide footnote on p. 859. 
