52 Coelenterata. 



finally the central zooids die, and we have an atoll in miniature. The basin 

 shaped reef grows until tide limit arrests its growth. Then the waves begin 

 to act upon it, producing coral debris. This becomes cemented into solid breccia 

 by deposition of calcium carbonate, forming a platform which arises first, and 

 remains best developed, on the windward side. Upon this crescent-shaped plat- 

 form the waves break at low tide and on to it some waves of unusual violence 

 will hurl fragments from the reef margin. Around such is deposited sediment 

 and this is the beginning of the island. On the lee side the waves will not 

 have force to construct a breccia platform so that the lagoon-entrance is situated 

 here. When the wind blows in opposite directions in different seasons, as in 

 the Monsoon area, the action may be equalised all round, and each constituent 

 island be a perfect atollon. In the Trade area, the uniformity of the wind will 

 produce a horse-shoe-shaped atoll, elongated in the direction of the wind, with 

 crescentic islands to windward. As waves wash over the breccia platform be- 

 tween adjacent islands the current is slowed and sediment deposited in stream- 

 lines from the ends of the islands, increasing their crescentic form. In the 

 middle of the interval the current sweeps on farthest and its burden of sand 

 is deposited in the lagoon opposite the entrance ; this accounts for those atolls 

 with most land to leeward and an entrance, guarded by a breccia platform, 

 to windward, for the sand, swept in from windward, is deposited on the lee 

 side of the lagoon blocking up the original entrance. The lagoon is gradually 

 obliterated by deposition of sand. If of large size, its windward side is first 

 obliterated. Fringing reefs arise upon those submarine slopes of oceanic land 

 that afford a foothold for corals above the limiting line of sedimentation. 

 Barrier reefs were rightly explained by Le Conte in 1856 as fringing reefs 

 limited on one side by muddiness of water and on the other by depth. See 

 also Gravierf 1 ). 



B. Alcyonaria. 



SeeCohn, Kinoshitaf 1 ), Kiikenthalp, 4 )? Marion, RouleH, Thomson & Crane(S 2 ). 



Harrison shows that Siphonogorgia and Chironephthya may be distinguished 

 by the form of growth and the mode of branching of the canal system. S. is 

 massive, rigid and brittle, with cylindrical stem and branches ; C. may or may 

 not have a cylindrical stem but the branches become flattened and deeply grooved 

 and the terminal twigs are much more slender. In the barren stem of S. there 

 is one large central canal and numerous small anastomosing solenia and the 

 whole coenenchyme is studded with numerous vertical spicules. In the branches 

 the main canal divides, each of its ultimate branches terminating in a coelenteron. 

 In the stem of C. there are about 8 canals, surrounding a mass of coenenchyme 

 practically without spicules ; outside them the coenenchyme is filled with spicules. 

 In the branches the canals become very large and as the coenenchyme is much 

 reduced the branch is grooved externally. The author retains the name Spon- 

 godes and describes 5 n. spp., she also describes Chirowphtfvya 9 (8 n., In. var.), 

 Siphonogorgia 2 (1 n.), Solenocaulon 2 (the spicules may fuse in places to form 

 a porous calcareous rod which may not be continuous). 



Kinoshita( 2 ) describes Filigella (diagnosis emended) 1 n. and Ads 3 (2 n.). 

 Three complete colonies of F. show no sign of having been attached or inserted 

 into sand, both ends have growing points. 



KUkenthalf 1 ) describes Euplexaura emend. 9 (2 n.), Anthoplexaura 1, Para- 

 plexaura n. 4 (2 n. spp., 2 n. nom.), Eunicella 2, Chrysogorgia 5, Melitodes 3 

 (2 var.), Acabaria 5 (1 n. var.), Acantliogorgia 4, Acalycigorgia 1. In Anihopl. 



