66 THE VOYAGE OF H.M.S. CHALLENGER. 
The species is close to the Pocillopora cespitosa, from which it can be distinguished 
by its more fruticose habit, its small cells, and the developed septa and columella. It is 
extremely close to the Pocillopora gracilis, which agrees with it in all essential particulars, 
and, differing only in the more slender habit, seems thus to be only a variety of the 
species. 
Locality.—Tongatabu. 
4. Pocillopora cespitosa, Dana. 
Pocillopora cespitosa, Dana, Zoophytes, p. 525, pl. xlix. fig. 5. 
s "1 Verrill, Proc. Essex Inst., vol. vi. p. 91. 
This species is exceedingly close to the Pocillopora brevicornis, though according to 
Verrill it is distinct from it. The typical form can readily be distinguished by its large 
cells (about or more than 1 mm. in diameter) and its thinner and more irregularly placed 
branches ; while the Pocillopora brevicorms is at the same time marked by its small 
cells (much less than 1 mm.) and its thickened, short, stumpy and close branches and 
branchlets. Not infrequently, however, the species takes on the short, suppressed growth 
of the Pocillopora brevicornis, when its cells become markedly smaller, and in this form 
it is extremely difficult to determine between the two species. 
A fragment from Tahiti, which is not separable from this species, is peculiar in the 
great size and depth of its calicles. These are occasionally as much as 2 mm. in 
diameter. 
Localities.—Reefs, Honolulu, and at depths from 1 to 2 fathoms ; Tahiti. 
5. Pocillopora brevicornis, Lamarck. 
Pocillopora brevicornis, Lamarck, Hist, Anim. sans Vert., i. p. 275. 
2 Dana, Zoophytes, p. 526, pl. xlix. fig. 8. 
A very fine specimen and some fragments were obtained. In many parts of the 
corallum the branches become rather slender and elongate, and take on the characteristic 
shape of the Pocillopora bulbosa, from which it is thus difficult to separate the species. 
Localities.—Api, New Hebrides ; reefs, Fiji. 
6. Pocillopora damucornis (Esper). 
Madrepora damicornis, Esper, Pflanz. Forts., i. p. 43; Madrep., pl. xlvi. A. 
A single rather large and more or less rounded clump was obtained, which agrees 
very closely with the figure and description given by Esper. The basal calicles are circular, 
