178 CEYLON PEARL OYSTER REPORT. 



Carter (56), who, however, did not adopt Gray's genus, but adhered to Bowerbank's 

 original name. 



In 1880, Carter (4) also described two species from the Gulf of Manaar, which he 

 named Microciona quadriradiata and M. quinqueradiata respectively, and called 

 attention to the resemblance of the echinating spicules in these species to those of 

 " Diclyocylindrus vickersii." It appears to me that all these three species must be 

 included in one genus, distinguished as in the diagnosis given above, for which we 

 may retain Gray's name Cyamon. 



This genus appears to be nearly related to Trikentrion, but is distinguished from it 

 by the absence of oxeote megascleres (compare Carter, 56). 



The peculiar radiate echinating spicule is probably derived from a spined echinating 

 stylus by great enlargement of three or four of the basal spines. In this way it may 

 come to resemble a tetractinellid spicule or an aster. It is extremely interesting to 

 compare with these forms the equally peculiar echinating " grapnel " spicule of 

 Acarnus, in which a tetractinellid form may also be arrived at secondarily, but by 

 enlargement of spines at the apex instead of at the base of the spicule. 



Cyamon quinqueradiatum (Carter). 



1880, Microciona quinqiieradiata, Carter (4). 



The single specimen in the collection forms a sub-circular crust, about 1 1 millims. in 

 diameter and 3 millims. thick in the middle, attached to a mass of nullipore.* The 

 surface is uneven and irregularly conulose, and there is in parts a distinct, thin 

 dermal membrane. In parts also the surface is sparsely hispid from the projection of 

 some of the large spicules. The texture is soft and compressible, internally somewhat 

 cavernous, and the colour (in spirit) is pale yellowish-brown. 



The skeleton consists chiefly of tylostyles and styles of various sizes, the latter (at 

 any rate usually) longer than the former. These spicules sometimes have their bases 

 resting on the substratum and sometimes they are arranged in short plumose columns ; 

 some have their apices projecting for a considerable distance beyond the surface. 

 The echinating spicules are rather scarce and local in their distribution, mostly to be 

 found amongst the bases of the other spicules ; though plentiful here and there, they 

 might easily be overlooked except in fortunate preparations. 



The spiculation agrees fairly closely with Carter's description, but I think he has 

 laid too much stress upon the distinction of the various forms of styli and tylostyli. 

 In our specimen these pass gradually into one another; the slender " acuate " is not 

 recognisable as a distinct type (it may be simply a young form), while the tylostyli 

 have larger heads than appears from Carter's description and figure. There may be 

 either three or four smooth rays in the echinating spicule (in addition to the spined 

 ray), but it agrees very closely with Carter's description and figure. 



R.N. 270 (deep water off Galle and onwards up West Coast). 



* In association with a small specimen of Petromica massalis, R.N. 269. 



