858 Proceedings of the Royal Society 
flat; but every now and then occurs a bed of Madrepora having 
the living tips of its branches bared by the retreating tide. Small 
nobs and bosses of Pontes * (P. tenuis , V., and gaimardi , E. & H.) 
lie loose on the sand. Tufts of that fragile coral, Seriatopora 
pacijica (Br.), are to be occasionally seen. Numerous molluscs, 
annelids, and echinoids find a home in the blocks of partially dead 
massive corals. Holothurians, star-fishes, and sea-urchins lie in 
numbers on the sand ; while those singular algae, Halimeda opuntia 
and Caulerpa sp., grow on different parts of the flat. 
I now come to the description of the weather margin of a reef in 
these islands. Traversing a surface formed of loose fragments of 
dead corals, aptly compared with a bed of clinkers, one stands 
wuthin the wash of the breakers, which even in the calmest weather 
hurl themselves with apparently irresistible fury against the reef. 
A gradual slope of comparatively bare rock, furrowed by fissures or 
channels and descending to a depth of 4 or 5 fathoms, receives the 
wash of the breakers.! With the exception of a tiny clump of a 
Pocillopora or a Stylophora, or a large dome-shaped mass of a 
Meandrina or a Coeloria , that may be occasionally exposed during 
the recoil of the waves, this sloping surface is largely bare of living 
coral. It is only in the fissures which traverse the slope that the 
corals may be truly said to thrive. Here the Stylophora (sp. 
mordax, D.) and the Pocillopora J that were just mentioned, attain 
to some size. Here also flourish small masses of a Porites, and a 
Cceloria, an encrusting Montipora , compressed tufts of Madrepora 
appressa (D., var.), and a bossy Madrepora hitherto undescribed. 
As I have already indicated, the large massive corals are only 
occasionally to be seen in the wash of the breakers. They prefer 
the less accessible part of the reef, beyond the first line of rollers. 
In truth, it may be generally stated that corals do not thrive in the 
break of the trade-swell in these regions. They are only to be 
found in luxuriance on the slopes of the declivity that is usually 
situated in depths between 5 and 15 fathoms, a declivity which 
may be truly termed the growing edge of the reef. § Now and then, 
* One that I found had enclosed or grown around a piece of pumice. 
+ Vide p. 883, where this gradual slope is described as a constant feature of 
the outer side of a reef in these seas. 
+ An undescribed species. 
§ Vide p. 883. 
