350 J. E. Duerden — Jamaican Actiniaria ; Parti. — Zoanthew. 



microscopic structure, the Jamaican specimens appear to agree very closely, 

 particularly so in the peculiar mesoglceal 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, Duchassaing and Michelotti, 1860. 



Brachycnemic Zoanthese, with a single mesoglceal sphincter muscle. Solitary, 

 or connected by ccenosarc. The body -wall is incrusted. The ectoderm is usually 

 discontinuous, but may be continuous. Lacuna? and cell-islets are found in the 

 mesoglcea. Dioecious or monoecious. 



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. xviii. a, fig. 8). 

 It has already been shown (1891, p. 623) that a similar monoecious and dioecious 

 condition exists in the genus Zoanthus, and doubtfully in Isaurus. 



Gemmaria variabilis, n. sp. 

 (PI. XVII. a, fig. 5.) 



Form. — Polyps erect, firm, smooth, arising independently from a lamellar 

 ccenenchyme, 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 disc 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 



