374 J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthece. 



deeply staining nuclei are arranged in a middle zone; narrow nematocysts occur 

 and large deeply staining granular gland-cells. The mesoglcea is very narrow. 

 The endoderm is thick and crowded with pigment spheres. A sulcar groove 

 occurs, and here the mesoglcea is much thickened, but contains no cell-enclosures. 



Mesenteries (PI. xx., fig. 6). — Twelve pairs of mesenteries, macrocnemic in their 

 arrangement, are present. In the upper region each is a little narrow at its 

 insertion in the column-wall, but the mesoglcea thickens rapidly ; only for a short 

 distance in the oesophageal region, but more below. In the perfect mesenteries, 

 the mesoglcea beyond is very thin, and appears to alter in character so that it takes 

 the stain better. There are no basal canals nor any cell-enclosures in the upper 

 region ; but lower two or three short canals, or there may be only cell- enclosures 

 with pigment granules, appearing in . the thickened part of the mesenteries. 

 The endoderm is like that of the column-wall. Below the oesophagus it thickens 

 enormously, and contains much pigment and granular matter ; the mesenterial 

 filaments are well developed and branched. In these, the zone of nuclei stains 

 deeply, and occasional very deeply staining glandular cells are present along with 

 nematocysts and much pigment matter. The parieto-basilar muscle is well marked 

 on each side of the mesentery, extending a very little along the column-wall. In 

 the imperfect mesenteries, the musculature extends the whole way round ; in the 

 perfect mesenteries, scarcely any distinction can be made in the musculature of 

 each side, and the mesoglcea is finely plaited. 



Gonads (PI. xx., fig. 6). — All the specimens examined from one colony con- 

 tained abundant ova, present only on the perfect mesenteries, and associated with 

 much pigment matter and enormously thickened endoderm. 



Coenenchyme and Base (PL xx., fig. 5). — The proximal surface of the base and 

 ccenenchyme, in contact throughout with the sponge, has a thin ectoderm crowded 

 with yellow pigment granules. The ectoderm of the upper surface of the ccenen 

 chyme is thick, and resembles that of the column-wall. 



The mesoglcea is rather thick, and its inclosures are similar to those of the 

 column- wall, but with a larger proportion of sponge spicules ; cell-inclosures are 

 numerous, and contain pigment granules. The endoderm of the base of the 

 polyp is very thin, and contains pigment spheres and granules. 



This species was first described by Duchassaing and Michelotti from specimens 

 obtained at St. Thomas. Of their figures (references to which are omitted from 

 the " Explication des Planches"), fig. 18 gives an approximate representation of 

 the appearance of the colonies on the sponge ; but fig. 17 is probably erroneous in 

 the number and appearance of the capitular ridges and furrows indicated. 

 Eight of these are shown, while in every case I have found twelve. In their later 

 paper (1866, p. 138) they state the number of tentacles to be twenty -four, and 

 arranged in two series ; and it is generally found that the capitular radiations 



