ACANTHASCUS. 189 



primary termmals, left unfilled by the siliceous deposit Avliieli 

 solders these togetlier {cfr. p. 1 IG). 



The free terminals at the end of secondary principals are always 

 rougli, tliougii often obsQletely so. The minute terminal discs are 

 either simple like pinheads or else toothed at the margin. The 

 general size of discoctasters and the proportion and shape of 

 their parts are of great systematic value and may he utilized 

 in distinguishing the different species. It frequently happens 

 that in one and the same species the deeply situated discoctas- 

 ters are considerably larger than those in the periphery of 

 the wall. 



The Wiicrodiscoliexaslers are minute and extremely delicate 

 rosettes of the usual structure. In general shape they seem to 

 be uniformly spherical, measuring under 40 !'■ in diameter. In 

 some species the diameter is only about 15/<. Not that they have 

 been o1)served in all Acanthascine species, for several species have 

 been found to be without them, though it is difficult to decide 

 in all cases if that negative result was not due simply to oversight 

 or to the individuality of the sponge. 



ACANTHASCUS F. E. »Sen. 



llypudermalia, diactins only; at any rate, no pent- 

 actins amongst them ; hence, never veiled. 



