MATTHAI— RECENT COLONIAL ASTR^ID^ 119 



Corallum. Massive, convex. Corallites penta- or hexagonal, often drawn out for 

 fission. Inter-calicinal vpalls thinner than in G. solida, never more than "75 mm. Cahces 

 ahout 4 mm. in diameter, depth 2 — 3 mm. 



Septa sloping gradually to a short distance, then dipping vertically ; edges serrate, 

 sides rough ; total number 18 — 22, usually meeting the rudimentary septa in neighbouring 

 corallites ; 7 — 1 1 septa meeting columella. Clefts behind paliform lobes sometimes 

 extending below level of columella. Columella spongy or dense, -^ — \ width of calyx, 

 sometimes quite rudimentary. 



Polyps. (1) In the stomodeeal region of polyp, subsidiary couples of mesenteries 

 about three or four times the number of principal couples. (2) In the same region, 

 entocoelic pleats narrow, slightly constricted at their bases, occasionally sub-divided and 

 restricted to outer one-third of width of principal mesentery ; pleatal region thicker than 

 in G. solida. (3) Nematocysts II h much fewer in the terminal tentacular batteries than 

 in G. solida. (4) Nematocysts II c with the dark-stained axis in each about three-fifths 

 length of the sac. 



Polyps examined 14, 3 and 2 fi-om two specimens from Hulule, Maldives, 2 from 

 a Ceylon colony, and 7 from five Rotuma colonies. 



Remarks. A. Polyps. 5 or 6 principal couples of mesenteries are present, of 

 which 1 — 3 are incomplete, and as many subsidiary couples as in G. solida. The pleatal 

 region of the mesenterial mesoglaea, when compared with the very thin non-pleatal region 

 is much thicker than in any species studied ; below the stomodeeal region of polyp, the 

 entocoelic pleats become broader and sub divided and extend over the outer half or two- 

 thirds of the width of the mesentery. The convolutions of the mesenteries are scarce, 

 hence the inter-mesenteric chambers appear more or less empty. 5 or 6 sub-terminal 

 batteries are present on the tentacles. The stomodseum is narrower than in G. solida, its 

 diameters being '75 mm. and "65 mm. Its ridges are thicker than broad, and tend to 

 unite in the upper half of the stomodaeum, two belonging to mesenteries of adjacent 

 couples forming each compound ridge. Nematocysts I and III rarely occur in the ridges. 

 Nematocysts I and II c are found occasionally in the straight regions of the mesenterial 

 filaments, while in their convolutions types II c and III occur in large numbers, the axis 

 of the former being somewhat bent into a drawn out 8. The calicoblastic layer of ecto- 

 derm is vacuolated and deeply columnar near the skeletal attachments of the mesenteries. 

 The endoderm is vacuolated everywhere ; in the oral-disc it is thicker than the overlying 

 ectoderm, resembling that of Favia i^entagona in that the algee are not closely arranged 

 and the nuclei gathered along its peripheral region ; on the mesenteries the endoderm 

 is very thin on either side of the non-pleatal region, swollen in the pleatal region where 

 the vacuoles ai-e arranged in the form of a row of oval sacs on either side, conspicuously 

 swollen (pad-like in transverse section) behind the filaments. Gonads were not present in 

 any of the polyps. 



B. Corallum. In Lamarck's collection in the Paris Museum is a small specimen 

 named Astrcea retiformis, Lam., on which apparently Lamarck founded his species. 

 A small specimen from the Red Sea, which Milne Edwards and Haime assigned to 

 Heliastrcea acropora, and which was later referred to G. favus by Klunzinger, resembles 



