340 J. E. Dueeden — Jamaican Actiniaria : Parti. — Zoantheai. 



diameter of capitulum in living retracted state 0'5 cm. ; diameter of disc in 

 extension 05 to 08 cm. ; inner tentacles 025 cm. long. 



Locality. — Jamaica : The commonest Zoanthus found around all the Cays. 

 It occurs in masses, covering large surfaces of the rocks and stones in shallow 

 water. Very often the polyps are almost embedded in debris of sand, mud, and 

 calcareous algse, so that in extension only the closely associated discs are exposed. 



Range. — Bermudas (M°Murrich); St. Thomas (Duchassaing and Michelotti). 



Column-wall. — The cuticle, sub-cuticla, and ectoderm are of the same character 

 as in the previous species. In preserved specimens the cuticle readily separates. 

 Abundant oval nematocysts are present in the ectoderm, especially in the distal 

 part. The boundary between the ectoderm and mesoglcea is not well defined, 

 cells and cell processes from the former passing into the latter. 



The mesogloea is broad in the region of the lower sphincter muscle, but 

 becomes thinner in both directions. It is without the empty lacunae below the 

 ectoderm, which are such a marked feature in the former ; large and small 

 spaces occur, the former containing but little cellular tissue and an occasional 

 nematocyst. In transverse sections a broken encircling canal is shown, in 

 some sections communicating with the ectoderm. Most of the cell-islets 

 throughout the mesoglcea contain fine pigment granules. The endoderm is 

 occasionally elevated between the mesenteries, and triangular in transverse 

 sections ; elsewhere it is very thin, and loaded with zooxanthellse. The 

 endodermal muscle is clearly distinguishable. 



Sphincter muscle (PI. xviii.a, fig. 2). — The form and arrangement of the cavities 

 of the sphincter muscle are best realized from the figure. It bears a resemblance 

 to the previous one, but the smaller proximal cavities are much more uniformly 

 and regularly distributed. The smaller cavities terminating the proximal half 

 are more numerous in some examples than in the one figured. In addition to 

 the lining muscle cells, rounded cells occur in the cavities. 



Tentacles. — The ectoderm is devoid of the cuticle and sub-cuticla. It is 

 made up of narrow columnar cells, with oval, deeply-staining nuclei, amongst 

 which are small oval nematocysts ; pigment granules and a weak ectodermal 

 muscle occur, the latter on very numerous, fine, mesoglceal plaitings. The 

 mesogloea is thin and a little plaited on the endodermal border for the support 

 of the circular muscle. 



The endoderm is very thick, leaving only a small lumen ; it is crowded 

 with zooxanthellse. 



Disc. — The disc is much like the tentacles in structure, but the endoderm 

 has about the same thickness as the ectoderm. 



(Esophagus. — In section, the ectoderm of the oesophagus shows three strongly 



