J. E. Durrpen—Jamaican Actiniaria: Part I.—Zoanthee. 361 
radiately. New individuals arise mostly along the side of those forming the 
periphery of a colony. 
Colour.—Ceenenchyme and column pale yellow or cream colour, sometimes 
brown; tentacles and furrowed portion of dise pellucid; middle of dise grey, due 
to presence of sand-grains ; lips white. 
Dimensions.—Average height of polyps 1:3 em., may be only 0°6 em. or 1°8 cm. ; 
diameter of flat expanded disc 1:2 cm.; average diameter of columns 0°6 cm. ; 
distance of centres of continguous polyps in retraction about 0°7 em. ; inner 
tentacles 0°2 cm. long. Colonies of various sizes are met with, but usually from 
3 to 8 em. across. 
Locality.— Jamaica: found in abundance firmly encrusting the coral-rock in 
shallow water, mostly in the region of the breakers, at the Cays outside Kingston 
Harbour, and at other points around the coast. 
Range.—Guadaloupe and St. Thomas (Duchassaing and Michelotti). 
Column-wall (Pl. x1x., fig. 1).—The column-wall of the individual polyps is 
separable from the ccenenchyme for only a short distance at the upper surface of 
the colony. The two are not very thick compared with the size of the polyps. 
In transverse sections the ccenenchyme may be from 0:1 to 0-2 cm. in thickness, 
while the polyps are from 0°6 em. to 0°3 em. in diameter. 
The ectoderm is a thick layer, and continuous over the outer surface of a 
colony ; a cuticle, devoid of foreign adhering matter, is present. Its internal 
limitations are occasionally irregular, due to the incrusting sand-grains; these 
latter are limited to the inner part of the ectoderm and to the mesoglea. The 
outer portion of the ectodermal cells is largely glandular; the middle and inner 
parts contain the nuclei, numerous zooxanthellae, and occasional large oval 
colourless nematocysts showing the internal thread. 
The mesogleea varies in thickness, appearing in sections as a matrix in which 
the cylindrical polyps are embedded. ‘The incrusting material is practically dis- 
tributed throughout; in the periphery of a colony however it is rather limited to 
the outer half. The foreign objects are mostly calcareous, but a few siliceous 
sponge spicules and an occasional Foraminiferal and Radiolarian test may be 
present. Abundant small and large cell-islets or short canals are distributed 
with considerable uniformity ; the latter in some sections exhibit somewhat of a 
concentric arrangement around the individual polyps, and may be seen communi- 
cating with the canals in the mesenteries. In others, a canal appears opposite 
nearly all the mesenteries. The islets contain zooxanthellz and large oval nema- 
tocysts; the smaller islets have the protoplasm exhibiting peripherally a fine 
morula-like appearance, with a central more deeply staining nucleus. A similar 
TRANS. ROY, DUB. SOC., N.S. VOL. VI., PART XIV. 31 
