334 
BULLETIN OE THE UNITED STATES EISH COMMISSION. 
Rather more chambers occur in the sphincter here represented than in the sphincter already 
figured in the account of the Jamaican polyps, and they are more closely arranged. Still the same 
general arrangement is presented in both; a certain amount of individual variation is to be expected. 
The ectoderm of the tentacles is an ordinary columnar epithelium, and unlike that of the column- 
wall is devoid of any cuticle and subcuticle. Very small nematocysts occur in a peripheral zone, and a 
weak longitudinal musculature on its inner border. The mesogloea is devoid of cell-islets, and the 
endoderm is greatly thickened in retracted examples, leaving scarcely any lumen and being crowded 
with zooxanthellse. A weak circular endodermal muscle occurs. 
The wall of the disk is much like that of the tentacles, but nematocysts are not so numerous in the 
ectoderm, and the endoderm is never so broad a layer. Numerous cells with granular protoplasm 
occur in the mesogloea, especially toward its ectodermal border. Both the endodermal and ectodermal 
musculatures are very weak. 
The stomodseum is usually greatly elongated in transverse sections, and the ectoderm forms about 
eight deep longitudinal folds on each side. The sulcar groove is smooth and elongated. Ciliated 
supporting cells are the principal constituents of the stomodteal ectoderm, but granular gland cells 
which stain deeply in methyl blue also occur, as well as a few nematocysts. The mesogloea is rather 
broad, and contains a few isolated cells. The endoderm is very narrow, as is the case with the lining 
of the coelenteron generally. 
The mesenteries are microtypic in all the polyps examined, the number of pairs varying from 
25 to JO. At their insertion in tlie column-wall they are narrow, but enlarge beyond, where the 
single basal canal occurs, the layer becoming very thin again. The basal canal is circular or oval in 
section in the upper region, but becomes more elongated below. A very weak parieto-basilar muscle 
occurs; the retractor muscle is clearly seen supported upon rounded folds of the mesogloea and enables 
the paired character of the mesenteries to be established. 
At the inner termination of the stomodseum the reflected ectoderm is very clearly seen, passing 
for a short distance up the face of the complete mesenteries and then downward along the free edge, 
giving rise to trifoliate mesenterial filaments. The character of the Zoanthid mesenterial filament has 
been fuliy described byMcMurrich (1899), and it is unnecessary to repeat it here. Shortly below the 
stomodteal termination the mesenterial endoderm becomes greatly swollen, the mesentery appearing 
clavate in transverse section. The epithelium is densely crowded with granules of various kinds, 
many of them yellow. McMurrich has surmised that the granules are in some way products of 
digestion. 
Many polyps from different colonies contained ova distributed about midway along the length of 
the macrocnemes. 
Localities. — St. Thomas (Ducliassaing & Michelotti) ; Jamaica (Duerden); Porto Rico (U. S. Fish 
Commission). 
Zoanthus sociatus (Ellis). Pis. II, IV, V; Figs. 4, 15-22. 
Actinia sociata, Ellis, 1767, p. 436, pi. xix, figs. 1, 2; Ellis & Solander, 1786, p. 5, pi. I, figs. 1, 2. 
Zoanthus sociatus, Lesueur, 1817, p. 176; McMurrich, 1889, p. 62, pi. ii, fig. 3; pi. iv, figs. 15-18; 1898, p. 242, pi. in, fig. 1; 
Verrill, 1900, p. 561. 
Zoanthus Jlos-marinus, Duerden, 1898, p.339, pi. xvii a, fig. 2; xvm a, fig. 2. 
External characters . — The polyps are erect, clavate or cylindrical in form, and rise directly from 
a thin band-like incrusting eoenenchyrne, or from a free irregular stolon, or directly from one another, 
either at the base or a short distance up the column. Usually the column is smooth, thin-walled, and 
pellucid, but sometimes a membranous cuticle occurs, more obvious toward the base, and foreign 
particles adhere to it. On complete retraction the column is usually swollen above, and on partial 
retraction a deep groove is seen separating the capitulum into an inner narrow zone and an outer region 
which passes insensibly into the column. Twenty-four to thirty minute rounded denticulations or 
capitular ridges, alternating with the outer row of tentacles, occur on the inner capitulum and are 
continued for some distance down the column. 
The tentacles are dicyclic, slightly entaemieous, smooth, acuminate or rounded at the tip, and 
overhanging in full expansion. They vary in number from 48 to 60. 
The disk is smooth, thin-walled, and shows radiating divisions. The peripheral area is more 
deeply grooved, and overhangs on full expansion; the middle region is elevated, and the mouth slit-like. 
