350 J. E. Durrpen—Jamaican Actiniaria ; Part I.—Zoanthee. 
microscopic structure, the Jamaican specimens appear to agree very closely, 
particularly so in the peculiar mesogloeal plaitings of the tentacles and the form 
of the mesenteries. 
Colonies obtained later from Port Antonio convince me that it will be found 
impossible to maintain the separation of the three species, to such an extent is the 
form variable in external characters and structure. 
Gemmaria, Ducuassaine and Micnevorti, 1860. 
Brachyenemic Zoanthez, with a single mesoglceal sphincter muscle. Solitary, 
or connected by ccenosare. The body-wall isincrusted. The ectoderm is usually 
discontinuous, but may be continuous. Lacune and cell-islets are found in the 
mesogloea. Dicecious or moncecious. 
The only difference between the definition of the genus here given and that in 
a former publication (1896, p. 142) is in connexion with the gonads. All the 
species hitherto examined have had the male and female reproductive cells, 
where present, in different individuals; but in the first representative described 
below, both ova and spermaria occur on the same mesenteries (PI. xvul. A, fig. 8). 
It has already been shown (1891, p. 623) that a similar moneecious and dicecious 
condition exists in the genus Zoanthus, and doubtfully in Isaurus. 
Gemmaria variabilis, n. sp. 
(BI XVi. «fie. 5.) 
Form.—Polyps erect, firm, smooth, arising independently from a lamellar 
ecenenchyme, or from around the base of one another, or may be solitary ; often 
cylindrical in retraction ; slightly enlarged and flattened distally, or occasionally 
narrowing and terminating bluntly; others, mostly long examples, are clavate, 
being narrow below and expanding above either slowly or more suddenly ; trans- 
versely wrinkled, especially in spirit specimens. Capitulum with about thirty 
ridges and furrows. Tentacles acuminate, arranged in two alternating rows of 
about thirty in each row; the number may vary considerably, forty in each row 
being counted in one example. Peristome considerably raised; the mouth 
elongated and slit-like. 
In full expansion, the capitulum and dise are much enlarged in proportion to 
the diameter of the column; and the individuals in a colony are so closely aggre- 
gated that, reaching the same level, the margins come in contact, and by mutual 
pressure produce a polygonal outline, leaving no interstices. Where examples in 
a colony incrust an irregular surface, or are fixed to the underside of stones, the 
