344 J. E. Dueeden — Jamaican Actiniaria : Part I. — Zoanthece. 



the cavities larger and more circular, as in the figures of the two previous 

 species. The sphincter in this species differs from that of the two former in that 

 the proximal part commences above with numerous small cavities. 



Tentacles. — The ectoderm of the tentacles is ciliated and without any cuticle 

 or sub-cuticla ; it is much thicker than that of the column, and small nematocysts 

 occur in restricted areas. The weak ectodermal muscle is supported on minute 

 plaitings of the mesogloea. The mesoglcea is thin, with a few isolated cells. 

 The endoderm is thicker than the ectoderm, leaving scarcely any lumen in 

 retraction. Abundant zooxanthellse, small oval nematocysts, and a weak 

 endodermal muscle are met with. 



Disc. — The ectoderm of the disc is nearly as thick as that of the tentacles ; 

 the nuclei stain very deeply ; an ectodermal musculature occurs. The mesoglcea 

 is broad, destitute of cell-enclosures, and contains a few isolated cells. The 

 endoderm is like that of the mesenteries, and has an endodermal musculature. 



(Esophagus. — The ectoderm in the oesophagus is rather broad and ciliated, and 

 thrown into about eight deep longitudinal folds on each side, partially followed 

 by the mesoglcea ; the oesophageal groove is elongated, occupying in some 

 sections about one-third the transverse area of the oesophagus. The appearance 

 is much the same as that figured by M c Murrich for the stomadceura of Z. sociatus. 

 The ectoderm contains an occasional small oval nematocyst, in addition to the 

 usual abundant narrow ones, and also a little pigment matter on its inner border. 

 The mesogloea is thinner than the ectoderm, and contains no cell enclosures. 



Mesenteries (PL xviii. a, fig. 4). — The number of mesenteries varies, twenty, 

 eight perfect ones occurring in one specimen, and twei:riy-six in another, corre- 

 sponding with the varying number of tentacles. A slight parieto-basilar muscle 

 is found on each side. The endoderm has zooxanthellse and small nematocysts. 

 A few isolated cells occur in the mesoglcea. Below the oesophagus, the mesen- 

 teries, with the mesenterial filaments, assume, in transverse section, first a sagittate 

 appearance, and lower a clavate form ; in the lower region of the oesophagus, 

 the reflected ectoderm has the characteristic pinnate appearance, the whole 

 corresponding with that described and figured by Haddon and Shackleton for 

 Z. M 'aegillivrayi (1891, p. 681). Nematocysts occur. 



A very weak musculature extends along the whole surface of both sides of the 

 mesentery, the mesoglcea being slightly plaited in places. A single basal canal 

 passes the whole vertical length ; in the perfect mesenteries, it is oval in section 

 in the distal region, but becomes elongated and stretches nearly the whole width 

 in the basal part of the polyp. 



In the imperfect mesenteries, the basal canal remains approximately circular 

 in section. The tissue inside the canals is of the same character as the endoderm, 

 being crowded with zooxanthellse and nematocysts. 



