50 Proceedings of the Royal Society of Victoria. 



placed tangentially and crossing one another in every direction, 

 or of similar spicules more or less collected into loose fibres. 



Megascleres, (a) long smooth tylostyli, with a slightly-developed 

 oval head at one end and gradually sharply pointed at the other ; 

 commonly more or less curved ; size variable, say about 0*54 by 

 0"007 mm. when fully developed ; (b) spined styli ; straight or 

 slightly curved, slender, gradually and finely pointed, covered 

 pretty evenly all over with small spines; commonly about 0*07 

 by 0"003 mm. but sometimes nearly twice as long. 



Microscleres, (a) smooth, straight, spindle-shaped microxea, 

 tapering equally from the middle to a tine point at each end ; 

 size about 0046 by 0'002 mm.; pretty abundantly scattered 

 between the sand grains and in the dermal membrane ; ib) very 

 slender smooth toxa varying immensely in length (measured up 

 to about 0"3 mm., but many only about 0'013 mm. long); 

 abundant. 



B.J^. 6; 501 (x, 20 f ; "drab, the projections ochre-yellow"); 

 683 (s. 9); 1045 (x B). 



Genus Acarmis, Gray. 



Megascleres styli and cladotylota (" grapnel-spicules "), to 

 which tylota may be added. Microscleres may be present in the 

 form of palmate isochela^ and toxa. 



Acarnus tenuis, n. sp. 



This species occurs in the form of small thin crusts on the 

 surface of other sponges. On one specimen of CJatliria typica 

 (R.N. 1072), for example, there are dozens of such crusts. They 

 are subcircular or irregular in outline, and the largest are only 

 about a quarter of an inch in diameter. They are thin and flat 

 and have no visible vents. In spirit they are of a pale yellow 

 colour. I have also found them on Plumohalichondria arenacea 

 (R.N. 974) and on Tedania digitata (R.N. 991). 



Skeleton, composed of a very loose network of irregularly- 

 interlacing spicules, with no visible spongin. 



Megascleres, (a) stylote or strongylote (perhaps sometimes 

 subtylostylote) ; straight, smooth, long and very sleiider, mea- 

 suring about 0-18 by 0*002 mm. ; comparatively scarce ; (b) clado- 

 tylote, straight (or nearly so), long and very slender ; with a 



