108 PERCY SLADEN TRUST EXPEDITION 



serrate edges, smooth or slightly rough sides, 17 — 24 in number, average about 20 ; 

 5 — 10 septa meeting columella, usually 6 — 8, exsert about "75 mm., most of them with 

 slender paliform lobes. Most of the subsidiary septa narrow. Usually an alternating 

 cycle of rudimentary septa present, recognisable only with a lens. Septa continuous from 

 corallite to corallite, their exsert ends being flat or slightly arched, giving a characteristic 

 appearance to the corallum. Columella usually rudimentary, formed of a few septal 

 trabeculse. 



Fission equal or sub-equal. 



A species showing comparatively little variation of the corallum. 



Milne Edwards and Haimes' type of Favia homhroni from "Oceanie?" is a large 

 specimen measuring 23 x 16 x 11 cm., in every respect resembling my examples. 



Localities. Maldives, Hulule (l). Minikoi (1). Chagos: Salomon (8). Also known 

 from Oceania (Milne Edwards and Haime), ? Sandwich Islands (Verrill). 



17. Favia vasta (Klunzinger). (PL 27, figs. 3, 5 and 6.) 



1879. Goniastrcea halicora var. obtusa, Klunzinger, Korall. Roth. Meer., iii, p. 33, pi. 4, fig. 2, and pi. x, 



figs. 3 a and b. 

 1879. Prionastrcea vasta, Klunzinger, Korall. Roth. Meer., iii, p. 38, pi. 4, figs. 8 and 12, pi. 10, figs. 4a and 6. 



Corallum. Massive, more or less flat. Corallites polygonal, usually hexa- or 

 pentagonal, with walls of neighbouring ones fused, the inter-calicinal partitions thus 

 formed 1 '5 — 2 "5 mm. in thickness. Calices widest at the calicular openings, with diameters 

 up to 22 and 15 mm., depth up to 13 mm. 



Septa sloping or with upper two-thirds or halves vertical and narrower, those of 

 adjacent corallites continuous over inter-calicinal walls, being exsert to 1 or 1'5 mm., with 

 edges well toothed, sides rough or sometimes smooth, up to 55 in number (average about 

 40); of these up to 24 meeting columella (average about 20), each with 8 — 10 teeth 

 becoming longer towards columella, the lower somewhat broader parts of the septa with 

 the longer teeth sometimes simulating a pali-crown. The subsidiary septa often curving 

 towards and fusing with sides of principal septa, up to 3 or 4 meeting one of the latter. 

 An alternating cycle of very narrow septa invariably present, those of neighbouring 

 corallites being continuous over inter-calicinal walls ; hence from surface a characteristic 

 alternating appearance of high and low septal arches. Columella formed of closely-twisted 

 trabeculse, often rising into points. 



Multiplication by marginal fission. 



Klunzinger has described two varieties of Prionastrcea vasta. In one (PL 4, fig. 12, 

 type measuring 8 x 7 x 4'5 cm.) the corallites are deep, with their diameters not very 

 unequal, the septa somewhat thin and the columellas well developed. Agreeing with this 

 are two of my specimens from Salomon (the larger measuring 13x8x4 cm.) with calices 

 about 20x15 cm. wide and 10 — 12 mm. deep (PL 27, fig. 5). These resemble Favia 

 abdita (Ell. and Sol.) in (l) marginal fission, (2) the subsidiary septa usually fusing with 

 the sides of the principal septa in groups of up to 3 or 4, (3) an almost equal number 

 of septal teeth of similar appearance to F. abdita, (4) the invariable presence of an 

 alternating cycle of very narrow septa, and (5) the columellae formed of closely-twisted 



