298 RKVISIO^S OF THE MONAXONID SPONGES, i., 



Between the "fibres,'' megascleres are scattered in profusion 

 and without apparent order. Spirasters likewise occur in all 

 parts, but onl}^ in moderate abundance (as compared with those 

 of S. australis) except at the surface, where they form a dense 

 layer varying in width from about 100/x to 450 /x, 



I'he tylostyli are typically straight, and are usually more or 

 less rounded off at the apex, so as occasionally to resemble tylo- 

 strongyla; the largest vary in length, in different specimens, from 

 440 /x to 560 /x and are about llyu, in diameter. The spirasters 

 are roughly divisible into two groups: (i.) those of larger size 

 and more regular and typical form, provided with large spines, 

 which comprise the majority of the microscleres scattered through- 

 out the interior of the sponge; and (ii.) those of smaller size and 

 variable form, with comparatively small spines, which chiefly 

 compose the dermal crust. The largest of the former measure 

 45 by 8/x, exclusive of spines: and their spines are, at most, IL' /x 

 in length. 



Remarks. — I have carefully examined many of the Cirripede- 

 shells that occur in the specimens of this species, but in no case 

 have I been able to detect (as in Cliona lutea) any sign of their 

 perforation by the sponge. 



Z/OC. — Port Jackson. 



Raphyrus hixonii. (Pl.xvi., figs.l, 2). 



This species, so far know^n only in the free or raphyroid stage, 

 is conspicuously characterised by a beautifully regular areolation 

 of the surface (PL xvi., fig.l), the areolae being circular in outline, 

 of diameter varying (gradually) over different parts of the surface 

 from 3 to 6 /x, and placed at intervals apart of from 2 to 3-5 /xf 

 the pattern of the areolation, when viewed from a distance, con- 

 sequently appears hexagonal. Judging from the material at my 

 disposal, which consists of some half-dozen large pieces of the 

 original specimens (including the piece figured by Lendenfeld), 

 and a small complete specimen obtained recently, the areolae — 

 except rarely and apparently abnormally — are situate on a level 

 with the general surface, and are distinguishable to the eye only 

 by reason of their difference in colour from the intervening areas; 



