PLATE 34. 



Hyalonema (Hyalonema) obtusum gracilis Lendenfeld. 

 Figures 1-19. 



1. — Section vertical to the surface, through a superficial part of the sponge; magnified 30; phot. Zeiss, 



planar 20 mm.: 



a, dermal membrane; b, subdermal cavities; c, a hypodermal pentactine with reduced and 

 terminally rounded apical ray. 



2. — Radial section through the choano.some ; magenta; magnified 100; phot. Zeiss, apochr. 16, compens. 



oc. 6. 



3. — Axial section through the oral cone and the adjacent parts of the upper end of the sponge; magenta; 



magnified 5; phot. Zeiss, planar 50 mm.: 



a, outer surface (dermal membrane); b, narrow fissure-like gastral cavity between the oral cone 

 and the oral frill; c, summit of the oral cone. 



4. — Axial section through the lower part of the sponge; magenta; magnified 5; phot. Zeiss, planar 50 mm. 

 5-18. — Choanosomal hexactines of the supporting skeleton; magnified 50; phot. Zeiss, achr. aa, oc. 2: 



5-7, 10, 12, situated with one axis (two rays) parallel to the optical axis, and two axes (four raj's) in 



a plane vertical to the optical axis; 

 8, 9, 11, 13-18, situated with the tips of three of the rays in a plane vertical to the optical axis; 

 5-7, 11, 15, 16, 18, medium-sized hexactines; 



8, 10, 13, 17, large hexactines; 



9, 12. 14, small hexactines. 



19. — Radial section through the superficial part of the sponge; magnified 100; phot. Zeiss, apochr. 16, 

 compens. oc. 6: 



a, dermal membrane; b, group of small macramphidiscs; c, subdermal cavity; d, hexactines 

 of the supporting skeleton. 



