MATTHAI— RECENT COLONIAL ASTRJEIDu^l 107 



principals, a group of 1 — 4 meeting a principal septum. Costse conspicuous when inter- 

 corallite grooves are present, with transversely extending granulations ; alternating with 

 these a cycle of smaller costse represented by very narrow septa in the thin-walled 

 corallites; costse of neighbouring corallites meeting in inter-coi-allite grooves, directly 

 continuous over walls when grooves are absent. Columella formed of closely-twisted 

 trabeculse, up to ^ width of calyx, usually -^ — ^ width. 



Multiplication by very unequal fission towards calicular margins. When walls are 

 formed round the small fission-products, they simulate buds. 



This species has a variable skeletal facies. Between the thin-walled polygonal level 

 corallites without surrounding grooves and the oval or circular thick-walled corallites with 

 distinct furrows there are many intermediate stages. (Compare PI. 26, figs. 5 — 7.) 



Gardiner's example (2) of Favia halicora, forma obtusa, is missing. 



Some of my examples from Salomon show a certain resemblance to Favia abdita in 

 having an alternating cycle of very narrow septa in every corallite and in fission being 

 marginal. The dredged specimen from Peros, Diamant, has further the hillocky mode of 

 growth so characteristic of Favia abdita. 



The two large specimens from Aldabra are identical with Ehrenberg's type of F'avia 

 halicora ( = Goniastrcea halicora var. acuta, Klunz.). 



In the two small specimens referred by Gardiner to forma acuta, Klunz., the inter- 

 calicinal walls are thinner (about 1 mm.), the calices smaller (about 6 mm. in diameter), and 

 the total number of septa is less (22 — 26) than in the large specimen which he assigned to 

 obtusa. Nevertheless, they belong to the present species. 



Ehrenberg's original of Astrcea halicora, which Klunzinger re-described and figured 

 as the type of Goyiiastrcea halicora var. acuta, is a large example (Mus. No. 733) 

 measuring 25 x 21 x 16 cm., in most parts without inter- corallite grooves. Identical with 

 this are my two large examples from Aldabra. The specimen from Ceylon which Ortmann 

 referred to Favia ehrenbergi measures 23 x 16 x 10 cm. 



Localities. Maldives: Hulule(l); Goidu(l); Turadu (1). Minikoi (3). Chagos : 

 Salomon (9); Egmont ? (1); Peros, Diamant (L from 15 fms.). Aldabra (2. from lagoon 

 reefs). Coetivy? (l). Singapore (l). Also from the Red Sea (Ehrenberg) and Ceylon 

 (Ortmann). 



16. Favia hombeoni (Rousseau). (PI. 26, figs. 1 and 2; 33, fig. 2.) 



1854. Parastraa hombronii, Louis Rousseau, Voy. au pole Sud de Dumont-d'Urville, Zool., v, p. 122, Zooph. 



pi. 28, fig. 3. 

 1857. Favia hombroni, Milne Edwards and Haime, Hist. Nat. Corall., ii, p. 435. 

 1866. Asfrea (Favia) hombroni, Verrill, Proc. Essex Inst., v, p. 33. 

 1904. Favia hombroni, Gardiner, Fauna Geogr. Maldives and Laccadives, ii, p. 771, pi. 62, fig. 27. 



Corallum. Massive, often becoming rounded off. Peritheca more or less compact. 

 Corallites polygonal, close together, with margins very thin when distinct, otherwise 

 inter-calicinal walls flat. Calices with diameters about 3 — 4 mm. and 2*5 — 3"5 mm., 

 depth 2 — 2 '5 mm. Calicular dissepiments about 1"25 mm. apart. 



Septa of even thinness along their entire breadth, with vertical, entire or finely- 



14—2 



