342 J. E. DurrpEN—Jamaican Actiniaria: Part I.—Zoanthee. 
aperture and numerous fine radiating capitular ridges; where the polyps are 
more separated, they often appear as low mammiform prominences. In partial 
retraction, a double capitulum is formed by the groove situated between the two 
parts of the sphincter muscle. In full expansion, the disc and capitulum are greatly 
extended, so that, when all the polyps in a colony are in this state, their margins 
are wholly in contact. The mutual pressure produces a polygonal outline, giving 
rise to the appearance of a mosaic work of green discs with elevated, often 
pink, centres, the two rows of dark short tentacles simulating a thick cementing 
material. Tentacles short, digitiform, overhanging in extension, arranged in 
two alternating rows of about thirty in each. The number may be slightly more 
or less. Dise depressed below the thickened margin; the mesenterial lines are 
seen through the wall; in expansion the oral cone is considerably elevated, and 
the mouth slit-like; the cesophageal groove is not obvious. The ccenenchyme 
is smooth, continuous, lamellar, adhering firmly to the rocks and stones, and 
following the larger irregularities of the surfaces. The polyps all arise inde- 
pendently, generally in close association, but may be further separated, when 
the ccoenenchyme becomes more ribbon-shaped. Owing to the thinness of the 
body-wall, there is often a partial collapse and transverse wrinkling in alcoholic 
specimens, especially in the more elongated examples. 
Colour.—Column in lower part of elongated forms is pale buff and transparent, 
with the white mesenterial lines showing through; upper part olive blue; 
capitulum lighter with green radiating lines, seen more especially on retraction. 
Tentacles, nearly always dark brown, may be green or olive. Disc generally 
a bright green, with light radiating lines corresponding with the internal 
mesenteries ; sometimes a pale green or yellow. In many, a darker triangular 
area extends towards the margin from each of the two extremities of the mouth ; 
one is often more pronounced than the other. (Esophagus green, with white lines 
showing through. Peristome in many colonies pink, in others a bright green ; 
more rarely yellow. An olive brown colour is first extracted by alcohol, 
leaving the colonies uniformly dark green, probably due to the abundant 
internal zooxanthellx; later the polyps become a buff colour, a little darker above, 
and the mesenterial lines show through. 
Dimensions.—Average diameter of column, 0°6 cm.; diameter of capitulum, in 
full expansion, 0:8 to 1 em.; length of column very variable, depending largely 
upon the position of the polyp in the colony, average length 1:3 cm.; some 
may attain a length of nearly 3 cm., while others extend only 0:4 em. above the 
ccoenenchyme. Tentacles 0:2 to 0:3 cm. in length. Colonies often 20 or 30cm. 
across. When preserved in alcohol, considerable contraction of the polyps occurs. 
Locality—Jamaica: Found in great abundance, forming large incrusting 
colonies on the rocks and stones in the shallow waters near the rocky parts of 
