Part II. — Stichodactylince and Zoanthece. 197 



but narrows rapidly beyond. A very short basal canal and several cell-islets 

 occur in the expanded portion. The mesenterial endoderm is broad and loaded 

 with zooxanthellae ; nematocysts also occur sparingly. 



Male gonads were present in all the numerous polyps sectionized from the one 

 colony. The surrounding mesenterial epithelium is enormously thickened and 

 the ripe spermaria are enclosed in the very thin mesoglcea. Around their 

 margin are the deeply-staining sperm mother-cells ; filling the greater part of 

 the interior are the heads of the ripe spermatozoa, while towards one side are 

 aggregated the tails of the spermatozoa (PI. xv., fig. 5). 



One very large, much-branched colony was trawled from a depth of 10-14 

 fathoms on the Pedro Bank, 11th April, 1898, incrusting an aborescent Plumtdaria, 

 as much as 100 cm. high. The coenenchyme was continuous nearly throughout 

 the surface of the Hydroid, only the smallest terminations being free. 



Apparently no Zoanthid at all resembling this form has been described from 

 Antillean waters, nor as a member of the nearly related Actiniarian fauna on the 

 western coast of Central and South America. 



In habit and external features it compares most closely with Parazoanthus 

 dichroicus, Hadd. and Shack. (1891, p. 698), obtained by Prof. Haddon from 

 Torres Straits, incrusting a specimen of Plumidaria ramsayi. It thus forms 

 another instance of the strong relationship, particularly in the Zoanthese, which 

 is being established between the Actiniaria of the Australian and Caribbean seas. 



The capitular ridges in P. dichroicus are about eighteen, an increase of two or 

 three beyond the number prevailing in P. tunicans. 



I have never observed any dichroic effect given to the alcohol from preserved 

 material, a peculiarity emphasized in the specific name of the former. Histo- 

 logically important differences are indicated, which leave no doubt as to the 

 distinctness of the two species. 



The incrusting particles of sand are siliceous in the older species and calcareous 

 in the new ; the encircling sinus is filled with dark-brown granular pigment in 

 the one, but not in the other. The latter distinction is associated with the 

 absence of zooxanthellse in the pigmented form, while they are abundant in 

 P. tunicans, which, conversely, is devoid of pigment. The mesenterial musculature 

 is less developed in the last-mentioned species. 



External characters alone readily separate it from all other known species 

 of Parazoanthus. 



Parazoanthus separatus, n. sp. 



(PI. x., figs. 12, 13 ; PI. xiii., fig. 8 ; PI. xiv., fig. 4.) 



In their retracted condition the isolated polyps present themselves as small, 



TRANS. KOY. DUB. SOC, N.S. VOL. VII., PART VI. 



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