Chap, xvi.] ALCVONARIAN CORALS. 



549 



bushes. On the shore were inclosures built by the Moros as 

 fish traps, to retain fish as the tide receded. In the shallow- 

 water contained in these traps were a large number of Medusae 

 of the genus Polydonia, all lying on the tops of their umbrellas, 

 with their tentacles directed upwards in full glare of the 

 sun. They looked, thus posed, like a lot of Sea-Anemones, 

 and I took them for such at first. They appeared perfectly 

 lively, and from time to time contracted their umbrellas. It 

 appeared almost as if they had assumed their position volun- 

 tarily, and were waiting for food in the same manner as 

 Actinias. * 



Alcyonarians (social Polyps, distinguished by having eight 

 tentacles), are extraordinarily abundant about the beach of 

 Santa Cruz Major. The reef rocks are covered with the soft 

 spongy forms of Alcyonarians ; they form extensive beds, which 

 are soft and boggy to tread on in wading. Amongst thee 

 grows a stony coral, which is likewise Alcyonarian, as I found 

 to my astonishment on examining its minute structure. It 

 forms thick erect plate-like masses which are of a chocolate 

 colour when living. The coral is remarkable because its hard 

 calcareous skeleton is of a bright blue colour instead of white, 

 as is usually the case. The coral is hence named Heliopora 

 ccerulea. It is, as far as is known, the only surviving represen- 

 tative of a large number of extinct forms of Palaeozoic age, 

 which are familiar in the fossil condition. It is nearly allied 

 to the well-known Red Coral of commerce. t 



Again, another interesting Alcyonarian is abundant, together 

 with those just described, namely, the red Organ-Coral 

 {Tubipora musica). There were cartloads of this coral, 

 dead and dried, lying on the beach, which was entirely com- 

 posed of various coral debris. The " Organ-Coral " was not 

 to be found living in shallow water on the reefs, but living 

 specimens were dredged from a depth of ten fathoms. 



Basilan Island, Feb. 4th and 5th, 1875. — The ship went for 

 a night to Port Isabella in Basilan Island, lying west of Zam- 

 boanga, to coal at the Spanish Government stores there. The 



* H. N. Moseley, " On the Structure and Relations of the Alcyonarian 

 Heliopora Ca;rulea," etc. Phil. Trans. R. Soc, Vol. clxvi,, Pt. i. 



t Polydonia frondosa has been observed in great numbers at the 

 Tortugas islands by A. Agassiz. They occur there in from three to six 

 feet of water, the disc resting on the bottom, the tentacles turned up- 

 wards. The disc pulsates slowly while they are at rest. When kept in 

 confinement they creep slowly over the ground by means of their 

 tentacles, and sometimes raise themselves edgeways against the sides 

 of the dishes, remaining stationary for a considerable time. 1 he peculiar 

 habits of Polydonia were noticed by Mertens in a species named by 

 Brandt P. Mertensii in 1838, and found at the Carolines. 



