172 THE VOYAGE OF H.M.S. CHALLENGER. 
Flabellum patens, n. sp. (Pl. VI. figs. 4, 4, 5, a). 
The adult corallum is wedge-shaped, with smooth sides. The form varies very much ; 
the lateral costee, which are sharp and more or less indented, varying in the angle which 
they make with one another between 100° and 160°. The inclinations of the lateral 
faces to one another vary from 30° to 50°. The surface of the corallum is smooth in 
very young specimens, polished, and of a red-brown colour; the principal costee are only 
just visible. There are distinct curved accretion lines in all the specimens, and in some 
deep transverse plications indicating a tendency to fission as in Flabelluim stokes, but 
this does not occur. There is a distinct short cylindrical pedicle. The summits of the 
short axis of the calicle are much higher than those of the long axis, and the lateral 
margins of the calicle describe even curves of nearly half a circle. The septa are very 
numerous, being doubtless added to in growth at the ends of the long diameter of the 
ealicle, as in Flabellum irregulare, Semper.’ In one perfect specimen there are 192 
septa of three sizes, twenty-four being complete, and, in appearance, equal and primary. 
In another more adult specimen there are 268 septa of four different dimensions, but 
the septa are a little irregular, and, at one end, the corallum has evidently had a 
considerable piece broken away, and this has been restored with a remarkable main- 
tenance of symmetry in the form of the corallum and septal arrangement. In another 
specimen there are 248 septa. The faces of the septa are covered with fine pointed 
granules. There is a deep elongate but narrow fossa well filled up at its bottom by 
columellar outgrowths. This coral is closely allied both to Flabellum stokesi and 
Flabellum pavoninum. It differs from Flabellum stokesi in not breaking away from the 
stock as growth proceeds, and multiplying by fission, and also in its more widely open 
form. In the young condition it is often very like Flabellum stokes’, indeed hardly 
distinguishable, but this fact is merely in accordance with the usual law of the likeness 
of the young of allied animals. From Flabellum pavoninum, Flabellum patens differs 
in having its faces less smooth than the former, and in having more septa. 
Extreme height of the ecalicle of a large specimen, 43 mm. Extreme breadth of the 
calicle, 55 mm. Shorter diameter of the calicle, 28 mm. 
Station 192, off the Ki Islands. 129 fathoms. Six specimens. 
Flabellum stokesi, Milne-Edwards and Haime (Hist. Nat. des Cor., vol. ii. p. 96). 
Flabellum variabile, Semper, Z. £. Wiss. Zool., 1872, p. 245, = Flabellum oweni, Flabellum 
aculeatum, and Flabellum spinosum, all of Milne-Edwards and Haime, /.c. 
Professor Semper, in his memoir entitled Ueber Generationswechsel bei Stein- 
korallen, shows the identity of the three above-cited species of MM. Milne-Edwards and 
Haime, and their relations to one another in development. One of the original names 
1 Semper, Generationswechsel bei Steinkorallen, Z. f. Wiss. Zool., 1872, p. 242. 
