8 ART. 7. — T. IJIMA '. HEXACTINELLIDA, IV. 



The oxyliexactins are numerously represented in tlie paren- 

 chyma and play an important part in the formation of the sup- 

 porting skeleton. Though somewhat variahle in size, most of them 

 are of moderately large dimensions. They may l:>e so large as to 

 present an axial length of nearly 2mm., the thickness of rays 

 reaching up to 30/^ near the central node. All the six rays are 

 not always of the same length. As a general rule, the spicules 

 lie with one of the axes directed radially and are met with in a 

 layer, — at places in a few ii-regular layers, — in the thickness of 

 the choanosome. 



The oxydiactins likewise occur in considerable numbers. They 

 are here decidedly more numerous than in Leucopsacus, but not 

 so numerous as in the 2;eneralitv of Kossellid members in which 

 diactins form the predominant, if not the only, megascleric ele- 

 ments of the parenchymalia. In the present species, the spicules 

 in question are mostly thin and small, not exceeding 22/;! in thick- 

 ness near the center, which may or may not be externally marked 

 by an annular swelling. Some are seen to run in company with 

 the radial rays of parenchymal oxyhexactins or of hypodermal 

 pentactins ; but the majority seem to j)ursue a in ore or less 

 paratangential ly directed course, either isolatedly or arranged in 

 bundles, which are strongest in the stalk-like basal region of the 

 sponge. Here a diactin may reach a length of 3 or 4mm. 



Close to the attachment-surface there occur a number of 

 stout-rayed and ytrickly-surfaced hexactins of about 100 /'• axial 

 length, forming a thin layer. The same spicules are occasionally 

 pentactinic and even stauractinic. There can be no doul)t that we 

 have here to do with the basidictyonalia. Some of the spicules 

 are loosely disposed ; others, especially those in direct contact with 

 the substratum, are joined together by synapticulœ in an irregular 



