J. E. DuerpEn—Jamaican Actiniaria: Part I.—Zoanthee. Shy6 
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, Lamourovux, 1816. 
Brachyenemic Zoanthez with a single mesogloeal sphincter muscle. ‘he 
body-wall is incrusted. The ectoderm is continuous. The mesoglcea contains 
numerous lacunz, and occasionally canals. Dicecious. Polyps immersed in a 
thick eccenenchyme, 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 coenenchyme, 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 
