1876.] 



Structure of the Stiflasteridcs. 



95 



are flattened like the stem from before backwards, and tend to coalesce 

 by their lateral margins and assume a flabellate form, which is some- 

 times somewhat curved. The surface of the corallum is perfectly even 

 and smooth, and pierced by deep calicular cavities, simply circular in 

 outline, and of two kinds, large and small. The larger less numerous 

 calicles are disposed at irregular intervals over the surface ; they are very 

 deep, reaching nearly to the centre of the axis of the branch or stem, and 

 contain a deep-seated, very long, and slender style with a brush-like tip. 

 The more numerous smaller calicles vary in size ; they are thickly dis- 

 posed between the larger ones ; they have no style. Seated beneath the 

 surface between the calicles are numerous ovoid cavities, the ampullae, 

 which in this genus do not project ; at certain stages of development 

 these communicate with the exterior by minute irregularly shaped pores, 

 seated in small shallow pits on the surface of the corallum. The calicles 

 are usually more abundant on one face of the corallum than on the other, 

 especially in its older basal region. 



Type of the genus Polyjpora dichotoma. 



Dimensions of the specimen : — Height of the corallum from 1| to 1 

 inch ; breadth of fan 6 inches ; diameter of stem from 1| to 1 inch ; dia- 

 meter of the mouths of the larger calicles -^-^ of an inch. 



A further examination of the species of Stylaster obtained off the 

 Meangis Islands was made in connexion with that of the corals referred 

 to above. This Stylaster resembles CryptoJielia in every particular, ex- 

 cepting that it has not the peculiar lid in front of its calicles. It will 

 have to be separated from the other Btylasters, and placed in the same 

 genus as Cryptohelia. 



Structure of the soft ^ arts of the Stylasteridce. 

 In all the Stylasteridao examined there is present an abundant coeno- 

 sarc, made up, as in the Milleporidse, of a network of anastomosing canals, 

 composed of an endoderm and ectoderm, and ramifying in corresponding 

 canals in the spongy trabecular calcareous coenenchym. In Polypora the 

 meshes of the network are comparatively close ; in all the other genera 

 examined far more widely open. In Cryptohelia and the Stylaster from 

 off the Meangis Islands, in which the cahcles appear as swellings seated 

 upon slender connecting branches, bundles of larger canals traverse the 

 axes of these branches, and connect the zooid groups of the several cali- 

 cles with one another. A continuous layer of tissue, as far as has yet 

 been seen without cellular structure, but containing thread-cells, covers 

 the external surface of the coenosarc in all the genera. In all the Stylas- 

 teridse there are two kinds of zooids, as in Millepora ; the larger and less 

 numerous have mouths and a special layer of digestive cells lining their 

 body-cavity. The more numerous smaller zooids have no mouths and no 

 gastric cells. The alimentary zooids are short and cylindrical ; the 

 smaller or tentacular zooids long and tapering. The alimentary zooids 

 in Stylaster erubescens have eight tentacles ; in Cryptohelia^ and in the 



