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XXX. — On a New Siphonogorgid Genus Cactogorgia * ; with Descriptions of 

 Three New Species. By James J. Simpson, M.A., B.Sc, Carnegie Research 

 Scholar, Natural History Department, University of Aberdeen. Communicated 

 by Professor J. Arthur Thomson, M.A., F.R.S.E. (With a Plate.) 



(Read November 19, 1906. Issued separately September 5, 1907.) 



Among the numerous littoral Alcyonarians collected by the Royal Indian Marine 

 survey ship Investigator in the Indian Ocean there are five small Siphonogorgids of 

 exceptional interest and apparently new to science. As some time must elapse before 

 the publication of the complete memoir on the Indian Ocean collection, it seems advisable 

 to make a separate report on these new forms. In so doing, I must acknowledge my 

 indebtedness to Professor A. Alcock, F.R.S., and Professor J. Arthur Thomson, M.A., 

 F.R.S.E., University of Aberdeen, for the opportunity of studying these interesting 

 forms, and to the latter also for much kind advice and encouragement. 



Systematic Position. 



The new type belongs to the order Alcyonacea, family Nephthyidse, and the excep- 

 tionally dense spiculation of the canal walls indicates its position in the sub-family 

 Siphonogorginse (Wright and Studer, Challenger Reports, Zoology, vol. xxxi.). In 

 certain respects it shows affinities with the Chironephthya-Siphonogorgia type, but the 

 following differences may be noted : — 



(1) The colony is much more densely spiculose, firm and rigid ; 



(2) There is a marked distinction into trunk and polyp-bearing portion ; 



(3) There is no definite branching, but the polyps are borne mainly on the margin 

 of flattened lobes. 



Generic Diagnosis. 



The colony is upright, with a basal attachment, and resembles a Cactus in its mode 

 of growth ; it consists of ( 1 ) a sterile trunk, very rigid and densely spiculose, in which 

 several small cylindrical canals are imbedded ; and (2) an upper polyp-bearing portion, 

 which in some cases bears expanded lobes. There is generally a flattening of the 

 polyp-bearing part and lobes, and the polyps are borne in several rows, for the most 

 part along the margin. The anthocodise are completely retractile within more or less 

 prominent verrucse composed of large spicules arranged longitudinally ; they are 

 comparatively large and bear a dense armature with a " crown and points " arrangement. 



* The generic name Cactogorgia is suggested by the general resemblance to a Cactus-type of growth. 

 TRANS. ROY. SOC. EDIN., VOL. XLV. PART III. (NO. 30). 120 



