340 J. E. Durrpen—Jamaican Actiniaria: Part I.—Zoanthee. 
diameter of capitulum in living retracted state 0°5 cm.; diameter of disc in 
extension 0:5 to 0°8 cm. ; inner tentacles 0:25 em. 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 débris of sand, mud, and 
calcareous algze, so that in extension only the closely associated discs are exposed. 
Range.—Bermudas (M°Murrich); St. Thomas (Duchassaing and Michelott1). 
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 mesoglea is not well defined, 
cells and cell processes from the former passing into the latter. 
The mesoglcea is broad in the region of the lower sphincter muscle, but 
becomes thinner in both directions. It is without the empty lacunz 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 zooxanthellae. The 
endodermal muscle is clearly distinguishable. 
Sphincter muscle (Pl. xvii. , 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, mesogleal 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 zooxanthelle. 
Disc.—The dise is much like the tentacles in structure, but the endoderm 
has about the same thickness as the ectoderm. 
Gsophagus.—In section, the ectoderm of the cesophagus shows three strongly 
