117 



(JOTON. R. Mice. Soc. 1908, pp. 075-81.) 



XX. — Note on a Eemarkahle Akyonarian, Stvderia * mirabilis 



g. et sp. n. 



By Professor J. Arthur Thom.sox, M.A. 



(Read November 18, 1908.) 



Plate XVI. 



A COLLECTION of Alcyonaiians made by the ' Investigator ' in the 

 Inriian Ocean incliideil a specimen from tlie Andamans wliich is 

 certainly one of the most remarkalile of the many interesting 

 representatives of tin's suh-class tliat have lieen discovereil within 

 recent years. It Ls a cup-like coh)ny, with a large retractile poly- 

 parium. The cup is 45 mm. in heiglit by 55 mm. in maximum 

 diameter, and it is continued into a ba.'^al wisp (19 nun. in length), 

 wliich, however, shows no attaching disk. The specimen gave 

 indication of having been imbedded in the mud u]i to about the 

 maximum diameter of the cup. 



General Structure. — The most striking peculiarity of this 

 Alcyonarian is that the whole of the polyp-bearing portion is 

 retracted within the exceedingly substantial, densely spinose cup, 

 the circular mouth of wliich is about 3(t nun. in diameter, and 

 shows the tips of numerous finger-like pol^ii-bearing lobes or 

 branches. It seems quite likely that the mouth of the cup was 

 capable of more complete closure, and, on tlie other hand, that the 

 retracted polyparium was capable of considerable protrusion. 



A longitudinal median section of the single specimen shows a 

 dome-shaped fleshy centre, or thalamus, from the margins and 

 summit of wluch most of the numerous finger-like jiolyp-bearing 

 lobes arise. Some of them, however, are attached to tlie inner wall 

 of the cup at different levels. The central dome, it should be 

 noted, rises quite freely in the middle ol' the cup ; its diameter is 

 greater than half the maximum <liameter of the cup. The arrange- 

 ment of the polyp-bearing lobes may be comparetl to the distribu- 

 tion of carpels and stamens in the flower of some of the Uosace<e, 

 in which the former are disposed on a dome-shaped central thalamus, 

 and tlu^ latt(>r on several whorls on the inner wall of the " calyx- 

 tube." Or, again, the central region of our specimen may be com- 



• I have named this type in honour of Professor Th. Rtuder, of Bern, who has 

 contributed so largely to our knowledge of .■Vlcyoiiaria. 



