170 CEYLON PEARL OYSTER REPORT. 



from the head to a fine, sharp apex. Spines rather small, conical and sharp pointed ; 

 on the head rather longer than elsewhere and arranged in a radiating manner, so 

 that the head, when viewed end on, resembles a spheraster. Size variable, up to 

 about 0'08 millim. in length by O'OOS millim. in thickness where the shaft joins the 

 head (exclusive of spines). These spicules are very numerous and, though quite 

 separate from one another, are placed pretty close together. 



(3.) Stout tridentate isochelas (Plate XI., fig. 5, c, d) of the usual Myxilla type, 

 with rather strongly curved shaft ; length about 0'032 millim. ; very numerous. 



This is a Myxilla, with the encrusting habit of a Hymedesmia, and with corre- 

 spondingly arranged skeleton. In spiculation it closely resembles TOPSENT'S Dendoryx 

 certa (48), but differs in skeleton arrangement, the spined styli forming a network in 

 the latter species. In fact, Myxilla tenuissima bears much the same relationship to 

 Myxilla (Dendoryx) certa that Rhabderemia pusilla does to Rhabderemia indica. 



R.N. 234A (on same mass as RN. 234, " deep water off Galle and onwards"). 



Clathria, SCHMIDT. 



Ectyoninaj of various habit, frequently clathrous ; skeleton a reticulation of fibre, 

 usually with much spongin, containing smooth styli and echinated by spined 

 styli. Typical microscleres small palmate isochelse, to which toxa are frequently 

 added. 



I have already (10) indicated the necessity for abandoning the genus Ithaphi- 

 dophlus of EEILERS, which differs from Clathria only in the possession of a dermal crust 

 of radially disposed styli. The degree of development of this crust varies to such 

 an extent, however, that it is quite impossible to base a generic distinction on this 

 character alone. 



Clathria frondifera (BOWERBANK). 



1875, Halichondria frondifera, BOWERBANK (49); 1884, Clathria frondifera, RIDLEY (16); 

 1889, Clathria corallitincta, DENDY (3). 



I do not think it is possible to keep the Ceylonese form, described by me under the 

 name Clathria corallitincta, separate from the common Australian and Indian Ocean 

 species, originally described by BOWERBANK from the Straits of Malacca and Gaspar 

 Straits under the name Halichondria frondifera and subsequently re-investigated by 



RlDLEY. 



The external form of the sponge is very characteristic, and one of Professor 

 HERDMAN'S specimens (RN. 44) bears a remarkably close resemblance to a specimen 

 from the Mascarene group figured by RIDLEY (loc. cit., Plate liii., fig. j). The 

 spiculation, however, seems to be somewhat variable, and I must add to the 

 description which I gave of Mr. THURSTON'S specimens the following particulars 

 concerning those in the present .collection. 



