352 KEVISION OF THE MONAXONID SPONGES, ii., 



when most abundant, the appearance of an irregular reticula- 

 tion extending between the fibres ; in this case, as in the pre- 

 ceding, the fibres are usually comparatively stout, being often 

 as much as 130/x or more in diameter, (iii.). The arrangement 

 of the scattered spicules is as in (ii.), but the fibres are slender, 

 20 to 70 fx in diameter, and run sinuously, with frequent inter- 

 osculation, (iv.) The fibres are rather slender and somewhat 

 distantly separated from one another, while the scattered spi- 

 cules are only moderately abundant, and are sometimes, in 

 considerable proportion, disposed more or less longitudinally. 



The first-mentioned type of arrangement is shown to best 

 advantage by the British Museum fragment above referred to, 

 labelled "Clathriodendroii irregularis" ; the second, by cer- 

 tain of the type-specimens of Tedania laxa; the third, also by 

 specimens of T. laxa; and the fourth, by the type-specimen 

 of Stylotdla digitata. The third type of arrangement, or 

 something intermediate between it and the first, is the com- 

 monest and most typical. 



The dermal membrane overlies wide subdermal spaces, and 

 is supported upon the extremities of short fibres* — branches 

 from the outermost of the longitudinal fibres — which are 

 directed towards it more or less perpendicularly. The dermal 

 skeleton consists of horizontally disposed spicules which, in 

 general, are either loosely scattered without order, or are 

 arranged somewhat in an irregular paucispicular network ; 

 around the oscula, however, they become more numerous and 

 are disposed radiately. Occasionally, fibres from the main 

 skeleton enter and run in the dermal membrane for a short 

 distance before terminating. 



The spicules are of a single kind, subtylostyli, usually with 

 only a very slightly developed oblongish head, which is marked 

 off by a scarcely perceptible constriction ; occasionally the head 

 is rendered more pronounced by a subterminal annular en- 

 largement. They are cylindrical throughout the greater part 

 of their length, taper gradually to a sharp point, and vary 

 from straight to curved (or sometimes flexuous) ; usually the 



