388 FUNAFUTI ATOLL. 



Colour. As per coloured sketch, drawn by Mr. C. Hedley on 

 the spot. Column pale green, capitulum pinkish, disc pale violet, 

 tentacles brownish-orange ; in formol, yellowish-grey. 



Dimensions. Length of largest colony, 7 cm. ; breadth, 5 cm. 

 Length of largest polyp, 1*7 cm.; diameter at base, 5 mm.; in the 

 middle, 7 mm.; at the capitulum, 11 mm.; diameter of disc about 

 8 mm. ; oral aperture, 3 mm. by 1 '5 mm. Length of tentacles 

 about T8 mm.; contracted examples are usually somewhat flat- 

 tened at the summit varying from 6 to 10 mm. in diameter 

 and frequently broader at the summit than long. 



ANATOMY. 



Body-wall (Plate xxvi, fig. 1). The ectoderm is thick, measur- 

 ing in breadth '07 mm., and forms a definitely continuous layer. 

 It is provided externally with a thin cuticle, to which occasional 

 diatoms adhere. A peripheral layer of mesoglcea is absent. 

 Numerous incrustations consisting of grains of calcareous sand, 

 foraminiferal shells etc., are present in the ectoderm and peri- 

 pheral portion of the mesogloea, forming a layer about '15 mm. 

 thick. Owing to the presence of these incrustations, the ectoderm 

 appears in decalcified sections considerably broken up, and is here 

 and there separated by a space, extending over a considerable 

 area, from the underlying mesoglcea. The ectoderm contains 

 zooxanthellae in considerable numbers and also numbers of large 

 nematocysts. One of the largest of the latter observed measured 

 1-35 mm. in length by -06 mm. in breadth, but their average size is 

 considerably less than this. 



As is characteristic of the genus, ectodermal canals are absent 

 from the mesoglcea. Large rounded or oval lacunae are, however, 

 abundant in the outer two-thirds of the layer. The lacunae con- 

 tain large nematocysts (usually one in each), similar to those of 

 the ectoderm and also contain numbers of zooxanthellae. Besides 

 lacunae small cell-islets and isolated cells produced into very dis- 

 tinct radial processes are present in the mesogloea. Except in 

 its most peripheral portion, below the ectoderm, the inesoglcoa is 

 almost completely devoid of incrustations. Occasional siliceous 

 spicules however do occur. 



The entoderm of the body-wall is thickened between the 

 mesenteries and contains zooxanthellae but they are here not so 

 numerous as in the ectoderm. The circular entodermal muscula- 

 ture is well developed. 



Capitulum. The outer surface of the capitulum is ridged, the 

 ridges alternating with the tentacles of the outer cycle. The 

 ectoderm is thicker than that of the column and is not so densely 

 crowded with incrustations. These are here more abundant in 

 the outer part of the mesogloea. 



