224 



PORIFERA 



Fig. 110. — Megascleres. a-l 

 and q-s, Modifications of 

 nionaxon type. «, Stroii- 

 gyle : b, tylote ; c, oxea ; 

 d, tylotoxea ; e, tylostyle ; 

 /, style ; g, spined tylo- 

 style ; h, sagittal triod (a 

 triaxoii form derived from 

 nionaxon) ; j, oxytylote ; k, 

 auatriaene ; I, protriaene ; 

 m, sterraster (polyaxon) ; 

 n. radial section through 

 the outer part of m, show- 

 ing two actines soldered 

 together by intervening 

 silica ; o, desma of an 

 Anomocladine Lithistid 

 (polyaxon) ; q, crepidial 

 strongyle, basis of rhab- 

 docrepid Lithistid desma ; 

 ?•, young form of rhab- 



docrepid desma, showing crepidial strongyle coated with successive layers of silica ; s, 



rhabdocrepid desma. 



33. 



34. 



35. 

 36. 

 37. 

 38. 

 39. 

 40. 



41. 



42. 

 43. 



rSkeleton reticulate or fibrous . . . . .34 



I Skeleton radiate or diffuse . . . . .37 



1 Skeleton with radiating fibres forming a reticulum with others crossing 

 [ them at riglit angles .... Quasilhna 



/"No microscleres . . . . . .35 



- Microscleres sigmata andV .^, -ii ^ ^ • i i ^ 



' =" ' toxa with or without trichodragmata 



Desmacella 



Microscleres signiata or j 



(Sponge fan- or funnel-shaped . 



(^Sponge not fan- or funnel-shaped 



C Megascleres slender and twisted 



\Megascleres somewhat stout, not twistt'd 



(Sigmata present, skeleton diffuse 



(Sigmata absent .... 



rSkeleton more or le.ss radiate 



^Skeleton diffuse ; sponge boring 



f Sponge discoid with marginal fringe 



(^Si)onge massive or stipitate without marginal fringe 



(Sponge body prolonged into mammiform projection; 



\Sponge body without mammiform projections . 



[No microscleres. Megascleres tylostyles witli or without styles 

 J Suberites 



[Microscleres centrotylote. Megascleres styles or tylostyles Ficulina 

 rChoanosomal megascleres smooth . . . .43 



\Choanosomal megascleres spined . . . Dendoryx 



(Microscleres chelae and sigmata of about the same size .Lissodendoryx 

 \ Chelae, if present, smaller than the signiata . . Yvesia 



. 36 



Hymcniacidon 



FhakelUa 



Tragosia 



Bicmma 



. 38 



. 39 



Clio n a 



. Halicnemia 



. 40 



I'ohjmasfia 



" . 41 



