214 TRANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



Calthrops, the actines 0*45 by 0*045 mm. (3) Ortho- 

 triaena, mostly deformed, rhabdome only slightly longer 

 than the cladi, of about the same dimensions as the 

 calthrops. (4) Anatriaena, fewer in number than the other 

 rnegascleres, projecting beyond the surface of the sponge, 

 with wide and distinct axial canal in rhabdome and 

 cladi, the rhabdome measuring 2*5 by 0*02 mm., the 

 cladi 0-09 by 0*02 mm. 



The Microscleres are of two kinds, (1) Smooth Microxea 

 present in vast numbers and forming a felted mass 

 throughout the whole sponge, 0*17 by 0*0035 mm., (2) 

 Spiraster, 0'02 mm. in length. 



Physcaphora decorticans, n.g. &sp. (PL XIII., figs. 2 & 3). 



The collection contains only a single fragment of this 

 highly interesting sponge, and that fragment apparently 

 represents only the ectosome of a tetractinellid sponge 

 which had become peeled off, as often happens in cases 

 where the cortex is highly developed. The specimen is 

 a thin flat piece, of stony consistency, measuring hori- 

 zontally 4 by 3 cm. and 0*5 to 1 mm. in thickness. The 

 surface is raised in minute conuli which may bear the 

 oscula at their summits. Its colour (in spirit) is yellowish 

 white or greyish, here and there rusty, in some parts 

 almost transparent. 



The skeleton consists of rnegascleres and microscleres. 

 The former are tylostyli, 0*51 by 0*008 mm., arranged in 

 bundles converging towards the surface of the sponge, 

 and raising it up in little conuli, and forming also a 

 support for the tissue round and below the oscula (PL 

 XIII. , fig. 3). The microscleres are of four kinds: (1) 

 Spiraster s, 0*014 mm. in length, forming a thin crust 

 along the surface of the sponge. (2) Spherasters, with 

 large centres and very short rays, forming a layer just 

 below the Spirasters, 0*012 mm. in diameter. (3) Spher- 



