188 J. E. DuERDEN — Jamaican Actiniaria : 



cUchroiciis, Hadd. and Sliackl., but histological characters reveal that the two are 

 quite distinct. I propose to term it Parazoanthus tunicans, on account of its 

 investing habit. 



Quantities of sponges were also trawled on the same occasion, many of which 

 displayed small commensal anemones distributed over nearly their whole surface. 

 On some massive, black sponges, two or three feet in diameter, the polyps 

 appeared as distinct, white, circular discs, but on a dark, purplish sponge they 

 were in small colonies, producing short catenulations. 



A detailed study discloses that these two, though somewhat similar in their 

 habit, are distinct species. 



Anatomical examination leaves no doubt that the first sponge-incrusting form 

 is a Parazoanthus, and I propose to term it P. separatus, in emphasis of the distinct 

 character of its individual polyps. With regard to the generic position of the 

 second, some uncertainty prevails. Owing to the remarkable shortness (0-5 mm.) 

 of the polyps, and the presence of numerous large sponge spicules in the capitular 

 region, I have failed to make out the arrangement of the mesenteries, or to 

 discover any sphincter muscle. 



Considering, however, the extreme weakness of the mvisculature in all the other 

 parts of the polyp, and the thinness of the mesogloea in the capitulum, there can 

 be no doubt that any sphincter occurring will conform to the type characteristic 

 of Parazoanthvis ; and further, comparing all its external and anatomical features 

 with those already known in other species, I have little or no hesitation in 

 assigning the form to the present genus. I propose for it the term Parazoanthus 

 monostichus, the polyps being usually arranged in a single row. 



A comparative study of the different representatives of the genus calls for a 

 few remarks of more general interest in Actinian morphology. 



In respect to both its musculature and the mesenterial filaments, Parazoanthus 

 displays conditions which lead one to place it as the lowest of the Zoanthean 

 o-enera, a position already assigned it by Haddon and Shackleton on less 

 conclusive grounds. Taking the mesenteries only into account Haddon considers 

 the other sub-family — the Brachycneminje — may be regarded as slightly more 

 primitive. 



The musculature in all the species of Parazoanthus is weak. This is especially 

 true of the sphincter muscle. In all other genera of the Zoanthidae the sphincter 

 is embedded in the mesogloea, and is usually of considerable strength ; in 

 Zoanthus it is even double, being subdivided into an upper and a lower portion. 



The difiuse, endodermal sphincter characteristic of the genus represents 

 merely a concentration in the capitular region of the circular endodermal muscle 

 which lines the column, usually throughout its length. 



As the sphincter becomes more strongly developed, the mesoglceal foldings 



