40 PSAMMASTRA. — THALASSOMORA. 



their rays are slender, straight, and cylindrical ; the whole spicule measures 

 0*0 1 millim. iu diameter. 



Geographical Distributiotst, — East coast of Australia: Poi-t Jaclisan 

 {Ramsay). 



Genus THALASSOMORA, n. gen. 



Stellettidae of spherical shape, without fibre-cortex. The centri- 

 petal ray of the tetract megasclera is longer than the tangential rays. 

 Microsclera of three kinds : small, spindle-shaped, and stellate 

 bodies in the int( rior ; and slender, rod-shaped, smooth spicules 

 projecting beyond the surface and perpendicular to it, causing; 

 the outer surface to assume a velvet-like appearance. 



Thalassomora nigra, n. sp. 



Spherical spongea, which are attached by a small base and attain a diameter 

 of 80-60 millim., a little broader than high, irregular and massive. Surface 

 pretty even and smooth ; in consequence of the projectiug dermal oxea, velvet- 

 like. Colour in spirit dark purple, nearly blaclv on the surface, light brown 

 iu the interior. The specimens are badly preserved and this colour is very 

 likely unuatural. 



There is no proper subdermal cavity : between the surface-tiifts of tetract 

 spicules very small cylindrical canals extend in a tangential direction ; these 

 have an average width of 0-08 millim. and are very numerous, they are 

 situated just below the surface. A little further down larger tangential canals, 

 with a more or less triangular transverse section, are met with ; these 

 have a diameter of 0-4 millim. In this lower zone also canals leading down 

 in a centripetal direction make their appearance ; these have an average 

 diameter of 0*17 millim., and from them, small irregularly tangentially extend- 

 ing canals originate, which have for the most part oval transverse sections. 

 The exhalants join to form curved oscular tubes with a circular transverse 

 section and a diameter of 1-2-5 mOlim. These tubes pervade the whole body 

 of the sponge, and give it in sections a somewhat bread-like appearance. The 

 oscula are small, only 1 millim. wide, scattered and not numerous. 



STceleton. — The supporting skeleton consists of large tetracts in the outer 

 layers and of monacts (oxea) iu the interior. The microsclera are of three 

 ]^JQc[s :— .(1) Tetract Megasclera. Abundant in the surface and just below it ; 

 absent in the interior. Angle between the centripetal and tangential rays ^=- 90° 

 (mostly =120°) ; centripetal ray 1*8 x 0-056 milHm,, conic, pointed ; tangential 

 ravs 0<3 X 0-05 millim., very slightly curved, conic, not sharp-pointed. — 



