8 CEYLON PEARL OYSTER REPORT. 



ami vrrv small, often vestigial cladome, which may be reduced to a mere knob. The 

 attachment of the cladome to the shaft is so slender that the former is generally 

 broken off and the spicules then may easily be mistaken for the well-known dermal 

 oxea of other species of Geodia. The proximal end of the shaft may be oxeote or 

 rounded off, or even tylote. In a typical example the shaft measures about 

 0'21 millim. by O'OOG millim. The cladome varies so much in its degree of reduction 

 that it is useless to attempt exact measurements, but is generally not more than 

 O'OOS millim. in total diameter. These spicules are found for the most part hispidating 

 the surface of the sponge, but a few occur beneath the layer of sterrasters. I have 

 seen one example which appears to be a reduced protrisene, with a single remaining 

 cladus, but the great majority are anatriaenes. 



(5.) Oxea (Plate III., fig. 3, d) ; very long and comparatively slender, frequently 

 curved, sometimes very crooked ; fairly gradually and sharply pointed ; size variable, 

 e.g., 2'5 millims. by - 029 millim. 



(6.) Sterrasters (Plate III., fig. 3, e, e' ; fig. SB, c) ; markedly oval in shape and 

 measuring about 0'12 millim. by 0'082 millim. 



(7.) Small spherasters (or chiasters?) (Plate III., fig. 3B, a); with small centrum 

 and numerous almost cylindrical or slightly tylote rays about as long as the diameter 

 of the centrum ; total diameter of the spicule tibout O'OOS millim. Most abundant in 

 the dermal membrane, but plentiful also in the interior. 



(8.) Comparatively large spherasters (Plate III., fig. 3, f; fig. SB, b); with large 

 centrum and very numerous short, conical rays, whose length is only about one-third 

 the diameter of the centrum or a little more. Total diameter when fully grown 

 about 0'024 millim. Sparsely scattered beneath the layer of sterrasters. 



In the structure of the ectosome and the presence of dichotria3nes this species is 

 evidently closely related to Geodia perarmata. It is, however, distinguished by 

 three characters : (l) the absence of brown pigment cells in the outer part of the 

 cortex ; (2) the form of the larger spheraster, which, in G. pcrarmata,, has (? always) 

 distinctly spined rays ; (3) the presence of the numerous short-shafted, cortical 

 auatrisenes,* which are replaced in G. perarmata by cortical oxea, though I am 

 inclined to think that a few of these oxea may still show a vestige of a cladome even 

 in G. perarmata, while it is quite possible that a few true cortical oxea may occur 

 amongst the reduced anatrisenes in G. peruncinata. 



The presence of the vestigial anatria3nes is extremely interesting as indicating the 

 anatrisenal origin of the cortical oxea of Geodia. SOLLAS (loc. cit., p. cxlvii) has 

 already observed, in his general remarks on the family Geodiidze, that " A second 

 finer hispidation is frequently produced by small oxeas, which are confined to the 

 cortex (cortical oxeas). Associated with these, in some few instances, are minute 

 anatriaenes, which much remind one of the cladose tylostyles described by DENDY and 

 RIDLEY in Proteleia sollasi." We have here an admirable example of the evolution 



* Very similar small cortical anatriasiies occur in LI.XDGKKN'S Geodia /Y//w'n.> from Cochin China (86). 



