374 



REVISION OF THE MONAXONID SPONGES, 11, 



90-155/jt. Those of the third group are the most abundant, while 

 those of medium size, which are the least frequent, are compara- 

 tively very scarce. Besides differing in size, the raphides of the 

 three groups exhibit, as a general rule, certain appreciable differ- 

 ences in other respects also, though all agree in being very gradu- 

 ally sharp-pointed at one extremity, and abruptly truncated at the 

 other, in being more or less spinulous, and in having the spinules 

 pointing in the direction of, and progressively increasing in size 



towards, the truncated or basal 

 end of the spicule. (i.) The 

 smallest raphides are conical in 

 shape, tapering gradually from 

 base to apex; are spinulous over 

 their entire extent ; and are 

 usually much less than 1 /x in 

 diameter. (ii.) The rather rare 

 raphides of intermediate size are 

 fusiform, with the region of great- 

 est stoutness nearer to the basal 

 end than to the middle of their 

 length; are provided over their 

 whole length with spinules which 

 attain to a larger size than those 

 of either (i.) or (iii.); and are 

 always relatively stout in pro- 

 portion to their length, their 

 diameter being seldom much less 

 than 2/x. (iii.) The longest 

 raphides are slightly fusiform, 

 with the region of greatest stout- 

 ness situated nearer to the 



m^ 



Fig. 12. 



T. digitata var. rubra, a, Styli. 



h, Tylota. c, Onychetse. 



middle of their length than to the basal end ; have a merely 

 roughened surface, or (as a rule, only in the case of the stoutest) 

 are perceptibly spinulous over their basal moiety only; are com- 

 monly terminated at their truncated end by a slender spine; and 

 vary in stoutness from less than 1 yu to slightly more than 2 /x. 

 Loc. — Port Jackson. 



