224 



PORIFERA 



Fig. 110. — Megascleres. a-l 

 and q-s. Modifications of 

 monaxon type, a, Stron- 

 gyle ; h, tylote ; c, oxea ; 

 d, tylotoxea ; e, tylostyle ; 

 /, style ; g, spined tylo- 

 style ; h, sagittal tried (a 

 triaxon form derived from 

 monaxon) ; y,oxytylote ; k, 

 anatriaene ; I, protriaene ; 

 " m, sterraster (polyaxon) ; 

 », radial section through 

 the outer part of m, show- 

 ing two actines soldered 

 together hy intervening 

 silica ; o, desma of an 

 Anomocladine Lithistid 

 (polyaxon) ; q, crepidial 

 strongyle, basis of rhab- 

 docrepid Lithistid desma ; 

 r, young form of rhab- 



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



epid desma. 



docrepid 

 rhabdocr 



33. 



34. 



35. 

 36. 

 37. 

 38. 

 39. 

 40. 



41. 



42. 

 43. 



(Skeleton reticulate or fibrous ..... 34' 

 Skeleton radiate or diffuse . . . . .37 



Skeleton with radiating fibres forming a reticulum -with others crossing 

 them at right angles .... Quasillina 



TNo mioroscleres . . . . . .35 



-! Microscleres sigmata and\ 



I , ,. , . . >toxa with or without trichodraemata 



Microscleres siemata or I t, ,, 



'^ D y Vesmacella 



("Sponge fan- or funnel-shaped . . . . .36 



\ Sponge not fan- or funnel-shaped . . Hyineniacidon 



("Megascleres slender and twisted . . . Fhakellia 



\Megascleres somewhat stout, not twisted . . Tragosia 



("Sigmata present, skeleton diffuse . . . Biemma 



\Sigmata absent . . . . . .38 



("Skeleton more or less radiate . . . . .39 



\Skeleton diffuse ; sponge boring . . . GKona 



("Sponge discoid with marginal fringe . . . Halicnemia 



\Sponge massive or stipitate without marginal fringe . . 40 



("Sponge body prolonged into mammiform projections . Polymastia 



\ Sponge body without mammiform projections . . .41 



("No mioroscleres. Megascleres tylostyles with or without styles 

 -! Suberites 



[Microscleres centrotylote. Megascleres styles or tylostyles FicuUna 



("Choanosomal megascleres smooth . . . .43 



\Choanosomal megascleres spined . . . Dendoryx 



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



Chelae, if present, smaller than the sigmata . . Yvesia 



