172 THE VOYAGE OF H.M.S. CHALLENGER. 



Flabellum patens, n. sp. (PL VI. figs. 4, a, 5, a). 



The adult corallum is wedge-shaped, with smooth sides. The form varies very much ; 

 the lateral costse, 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 costae 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 Flabellum stokesi, 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 

 calicle, as in Flabellum irregulare, Semper. 1 In one perfect specimen there are 192 

 septa of three sizes, twenty-four being complete, and, in appearance, ecpial 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 stokesi, 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 parens differs 

 in having its faces less smooth than the former, and in having more septa. 



Extreme height of the calicle 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. f. Wiss. Zool., 1872, p. 245, = Flabellum oweni, Flabellum 

 acukatum, and Flabellum spinosum, all of Milne-Edwards and Haime, I.e. 



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. 



