82 CEYLON PEARL OYSTER REPORT. 



typically sharp-pointed, but may be blunted. A typical example gave the following 

 measurements: shaft, I/O millim. by 0'0328 millim. ; protocladus, O'Oo millim. by 

 0'027 millim. ; deuterocladus, 0'065 millim. by 0'0164 millim. 



(2.) Protriaenes? 



(3.) Anatriaanes (Plate III., fig. 2, c, c'); with slender, often hair-like shaft and 

 small, variable, often abnormal cladome, perhaps characteristically flattened in front. 

 These spicules are evidently becoming vestigial and are so variable that it would be 

 useless to give measurements ; they are, however, still present in abundance. 



(4.) Oxea (Plate III., fig. 2, d) large and usually stout ; nearly always more or less 

 curved, often strongly so, sometimes crooked ; gradually and sharply pointed at each 

 end, or more or less blunted; measuring up to about 1'4 millims. by 0'049 millim., 

 but very variable in thickness. 



(5.) Chiasters, with short, blunt, sub-cylindrical rays (Plate III., fig. 2, c), total 

 diameter about O'OOS millim. ; very abundant in the dermal membrane, and often met 

 with in the choanosome, where they are commonly about half as large again and may 

 vary into oxyasters (?) with very slender rays (Plate III., fig. 2,y). 



(6.) Microstrongyla (Plate III., fig. 2, g) almost cylindrical, usually with rounded 

 ends, but occasionally oxeote ; minutely spined all over ; usually slightly curved ; 

 sometimes centrotylote. A typical example measures about O'l millim. by O'OOS millim., 

 but they are often much more slender. These spicules are found chiefly in the cortex, 

 but may also be met with occasionally in the deeper parts of the sponge. 



(A few slender, smooth microxea (Plate III., fig. 2, A) also occur, possibly young 

 forms of other spicules. ) 



There is no distinct fibrous cortex, at any rate over the general surface, but a dense 

 spicular cortex formed as described above. In the deep depression at the end of the 

 sponge, however, where the spicular cortex is not developed, a certain amount of 

 fibrous tissue is present in its place, and it is quite possible that such is also present 

 concealed between the spicules of the spicular cortex elsewhere. (These facts serve 

 to emphasise the unsatisfactoriness of the fibrous cortex as a generic distinction 

 between Edonema and Psammastra, to which attention has already been called 

 under the head of Edonema carteri.} The spicular cortex contains an immense 

 number of rounded pigment cells filled with pigment granules of a rich brown 

 colour. 



Scattered abundantly throughout the choanosome are rounded groups of minute 

 highly-refractive granules, staining with borax carmine, but in themselves practically 

 colourless. These at first sight look like flagellate chambers, each group being about 

 0'02 millim. in diameter, but I do not think that they are really of that nature. 



The species is evidently closely related to Edonema carteri and its allies, but is 

 well characterised by the dichotriaenes and by the comparatively large size of the 

 microstrongyles. 



RN. 265 (Station XL VI., off Mount Lavinia, 30 fathoms). 



