776 NEW GENERA OP MONAXONID SPONGES, 



Megascleres. — (i) The styli of the fibres (Text-fig. 1, a) are, 

 almost without exception, more or less curved, and of nearly- 

 uniform diameter throughout the greater part (not less than 

 two-thirds) of their length, tapering thence gradually to a 

 sharp point; as a rule they are slightly stouter in the middle 

 than at their base. Their curvature is generally greatest in the 

 case of the shorter spicules, and is such that the summit of 

 curvature is usually not very far distant from the mid-point of 

 the spicule. They vary rather considerably in size in the same 

 specimen, but not much as regards their maximum size in dif- 

 ferent specimens. In the particular specimen in which, of all 

 those examined, the megascleres were of smallest dimensions, 

 the range in size of the fibral spicules was from 130 X 6/x to 

 410 x 22 fx while in the specimen with the largest spicules it 

 was from 160 X 10^ to 465 X 26/*. The smallest of them, 

 up to an observed size of 230 by 13yu,, occasionally exhibit a 

 faint spinulation on the summit of their basal extremity, simi- 

 lar to (but much less distinct than) that which is characteristic 

 of the dermal spicules. Proceeding towards the outer extrem- 

 ities of the radial fibres, the fibral megascleres beccme gradu- 

 ally more uniform in size and of greater average length than in 

 the more interiorly situated fibres of the skeleton, and finally, in 

 the subdermal brushes, become indistinguishable from the next- 

 described or interstitial styli. 



(ii.) The styli composing the subdermal brushes and occur- 

 ring also in great numbers scattered interstitially (Text-fig. 1, 

 b ) , are invariably straight or nearly so ; are usually considerably 

 stouter near the middle than at the base; and taper (through- 

 out more than one-third, at least, of their length) gradually to 

 a sharp point. Amongst those occurring interstitially, how- 

 ever, there is comprised a complete series of forms, of pro- 

 gressively diminishing size, the smallest of which are identically 

 similar in every respect to the dermal styli. Their maximum 

 size varies in different specimens from aboul 520 X 13.5^ to 

 590 ; 16fx . The smallest spicules of which the form approxi- 

 mates more closely to that characteristic of the largest inter- 

 stitial spicules than to that characteristic of the dermal spicules 

 are usually not much less than about 240 x 10^ in size. Up to 

 this size, almost without exception, the interstitial spicules are 

 provided basally with a small cap of spinules; and even 

 spicules of considerably greater length are often similarly pro- 



