GARDINER—MADREPORARIAN CORALS. 281 
specimen closely resembling in its growth Studer’s figure of //. tiara), and in having 
their costal spines except near their edges more irregularly arranged, less closely packed 
together, and sometimes branched. All are much perforated, and the Chagos specimens 
are undoubtedly merely more densely and heavily grown forms of the same species as 
we obtained from the Maldives, with rather thicker septa and more definitely toothed 
and more radiately arranged coste, these characters probably being due to their form of 
growth. All have smooth-sided, almost glabrous costal spines and septa, the latter with 
coarse, irregular, deeply cut teeth, never secondarily toothed as shown in Dana’s figure 
of H. pileus. 
The Chagos specimens are as follows :— 
(1) A dome, about 22 em. high by 21X27 em. in diameter at its lower edges, central 
axial calicle at its summit well marked, edge at one point curiously turned in for about 
5 em. and partially fused together as if attempting to form a fresh corallum. The 
underside has a bare area in the centre where the corallum was formerly attached, and 
a series of concentric markings around the same. 
(2) A dome, about 15 cm. high by about 1612 cm. in diameter. It has no central 
calicle, but shows on the underside the point where it was formerly attached. This lies 
to one side, halfway between the edge and the summit. It is clearly shown that at one 
time it was a round disc, one side and much of the lower part of which got killed. 
The other side, however, grew out and, following its hereditary tendency of growth, 
formed a dome. It also subsequently commenced to grow down over the dead half of 
its own disc, a process not yet complete. 
Locality. Salomon Atoll, Chagos Archipelago, protected reefs of lagoon lying free in 
holes between large fixed growths of massive corals. Previously known from the 
Maldives and Philippines. There is also a specimen in the British Museum collected by 
G. C. Bourne at Diego Garcia. The related species, H. pileus, H. tiara, and H. concen- 
trica, according to Studer come respectively from Fiji, the Kingsmill and the Pelew 
Islands. There is also a Cambridge Museum specimen of H. pileus from Samoa, and a 
British Museum one of H. tiara from the Solomon Islands, collected by Guppy. 
V. Genus DODERLEINIA, gen. n. 
I have already sufficiently discussed the separation of certain forms under this genus. 
Its characters are as follows :— 
The corallum is thick and heavy, free, disc-like when young, gettirg arched later. 
Its wall is porous, freely so near the edge, filling up in the centre. It commences 
with a central calicle, but commonly breaks up as it enlarges, each fragment re- 
generating its corallum. Such growths are irregularly covered with calicles, each 
with from 6 to 12 distinct septa. 
The costze are low, distinct at least at the edge, subequal in size, set with low, 
rounded spines, all clearly and crowdedly granulated. The septa are alternately 
large and small, the latter being thinner and lower; they are muck granulated all 
over and the largest end in blunt denticulations. 
SECOND SERIES.—ZOOLOGY, VOL. XII. 39 
