J. E. Duerdest — Jamaican Actiniaria : Part I. — Zoanthece. 357 



The combination of characters in which Gemmaria fusca differs from G. varia- 

 bilis are : (1) the uniformly brown colouration, (2) the paucity of the incrustations, 



(3) the almost absence of basal canals in the upper part of the perfect mesenteries, 



(4) the appearance of the sphincter muscle, and (5) the generally more delicate 

 structure throughout. 



For some time I was inclined to regard these two species as being the same, 

 and it was not until an anatomical examination had been made that their dis- 

 tinction was fully apparent. The sphincter muscle, quantity of incrustations, and 

 other structures, are different. Externally they may be distinguished by their 

 colouration. Though not inclined to regard this character as very constant, 

 amongst numerous colonies I have met with no variations from the type in the 

 present species, nor wholly brown examples of G. variabilis. G. fusca is longer 

 and more regularly cylindrical than the other, without the same tendency to 

 assume a clavate shape. It is also less rigid, the body-wall not being so thick 

 and incrusted, and young individuals arise more numerously amongst the older 

 polyps. The colonies are smaller and less associated. 



Palythoa, Lamoueoux, 1816. 



Brachycnemic Zoantheae with a single mesoglceal sphincter muscle. The 

 body-wall is incrusted. The ectoderm is continuous. The mesoglcea contains 

 numerous lacunae, and occasionally canals. Dioecious. Polyps immersed in a 

 thick ccenenchyme, which forms a massive expansion. 



The above is the definition of the genus given by Haddon and Shackleton 

 (1891, p. 691), who also add a detailed history of its complicated career. 



In regard to the specific identification of its members, the genus Palythoa 

 has always been recognized by specialists as one of extreme difficulty and uncer- 

 tainty on account of its variability in form and the presence of only a few external 

 diagnostic characters. Especially is this the case when, as usually obtains, its 

 representatives are studied as alcoholic specimens in a condition of retraction and 

 shrinkage in variable degrees. Great danger exists under these circumstances in 

 the identification of isolated patches, or of even complete colonies. The external 

 characters one has usually to depend upon are those of the amount of the column 

 of the polyps free from the ccenenchyme, the dimensions, colour, wrinklings, number 

 of capitular ridges and tentacles. All these are, however, very inconstant ; only 

 when a number of examples are obtainable for comparison can much value be 

 placed upon them. 



The height of the free portion of the column is mainly dependent upon the 

 extent of retraction of the polyps, and is not a constant specific character. In 

 one portion of a colony the upper surface may be almost uniform, none of the 



