342 J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthea}. 



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. Disc 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 oesophageal groove is not obvious. The coenenchyme 

 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 coenenchyme 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 zooxanthellaj; later the polyps become a buff colour, a little darker above, 

 and the mesenterial lines show through. 



Dimensions. — Average diameter of column, 06 cm. ; diameter of capitulum, in 

 full expansion, OS to 1 cm. ; 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 04 cm. above the 

 coenenchyme. Tentacles 02 to - 3 cm. in length. Colonies often 20 or 30 cm. 

 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 



