182 J. E. Duerden — Jamaican Actiniaria : 



in outline, tough, and firmly adherent to various objects. Polyps are met with 

 in groups, and are occasionally found connected, one with another, by a thin basal 

 expansion or ccenosarc. The column is short, mammiform or cylindrical in 

 retraction, irregular in outline below, and circular or oval above. The surface is 

 smooth, and the walls thin and translucent, the lines of attachment of the 

 mesenteries showing through, and dividing the whole column into slight ridges 

 and furrows. 



The tentacles are arranged in cycles and in radiating rows, each row com- 

 municating with one mesenterial space. In one specimen in which the tentacles 

 could be counted they numbered 48, arranged in four cycles in the formula 8, 8, 

 16, 16. The innermost tentacles are very short, appearing as mere tubercles on 

 the disc ; the intermediate show a distinct stem and knob, while the outermost are 

 still larger, and overhang in extension ; the stems are conical, and the knobs 

 rounded. The disc is oval or circular, smooth, thin-walled, and nearly transparent, 

 the mesenterial lines showing through ; the oral cone may be very prominent. The 

 mouth is oval ; the walls of the stornodeeum are deeply ridged and furrowed, and 

 very protrusible ; no gonidial grooves are indicated. The disc and tentacles may 

 be entirely hidden in retraction. 



The column is brown below, and almost colourless or crimson above ; a circle 

 of small, emerald green, capitular spots may or may not be present. The stems 

 of the tentacles are translucent and colourless or yellowish ; the knobs rose, red, 

 or orange. The disc is brown, with white radiating lines ; the peristome bears a 

 narrow circle of emerald green spots ; the stomodseal wall is white. 



When retracted, the polyps measure about - 7 cm. in diameter, and are the 

 same in height. 



Anatomy and Histology. 



Examined histologically the ectoderm of the base and also of the column-wall 

 is remarkable for the abundance of large unicellular mucous glands, mingled with 

 the narrow supporting cells. They appear to constitute the greater part of the 

 layer, becoming more swollen towards the free surface, where they give rise to an 

 almost clear zone. The contents are sometimes clear and homogeneous, and do 

 not stain in borax carmine ; in most cases, however, they are finely granular, and 

 take up the colour slightly. The nuclei of the supporting cells are arranged in a 

 zone a little within the middle of the layer, while the most internal region of the 

 ectoderm exhibits nerve and muscle fibrils. The ectodermal musculature is 

 discernible on the base, but becomes stronger on the column-wall, the cut ends of 

 its fibrils appearing as a very distinct layer in transverse sections. 



Throughout the base and column-wall the ectoderm remains a high columnar 



