SPONGES.-HALLMANN. , ,0, 



Ihe acanthostyles bear a close resemblance to those ol C. 

 arbuscula and like them are divisible into two sizes. Their 

 lengths lie between 90 and 210 ;^, but individuals between 

 120 and 180 ;i in length have not been observed; the stoutest 

 are 12 ji in diameter. The isochelae arcuatJE differ from those 

 of C. arbuscula only in their slightly larger size; they measure 

 from 21 to 28 }i in length, with a maximum stoutness of shaft 

 of slightl}' more than 4.5 H- Whitelegge's description would 

 imply that the oxea do not occur as coring spicules, and that 

 the larger acanthostyles do not to any notable extent echinate 

 the fibres. The fact that he placed the species in the genus 

 Stylostichon would imply the same. Howe\'er, I find that 

 wherever the fibres are not so densely echinated as to obscure 

 the coring spicules, oxea in small numbers are usually to be 

 seen ; at the same time, the larger acanthostyles occur plenti- 

 fully as echinating spicules. Nevertheless, it must be con- 

 fessed that the occurrence of oxea in the fibres appears to be 

 more or less sporadic, and accordingly it would seem that no 

 hard and fast distinction can be drawn between Clathrissa and 

 Stylostichon. 



Plumohalicliondria ccespitosa (Carter), as identified b\ 

 Dendy,! is another species sufficiently closely related to C. 

 arbuscula to admit almost of its being regarded as a variety of 

 it. I have examined a slide of this sponge, presented to the 

 Australian Museum by Professor Dendy, and find that the 

 spicules are of the same general character as those of C. arbus- 

 cula. The oxea are slightly smaller, rarely reaching quite 

 as much as 4 fi in stoutness and varying in length from 

 150 to 200 f(. Acanthostyles of all lengths from 84 to^ 

 240 ;t occur, there being no actual separation into two sizes, 

 although spicules of intermediate lengths are of less frequent 

 occurrence. The isochela? arcuatae are 27 to 32 fi in length. 

 It will be noticed that the lengths of the two last-mentioned 

 spicules are much greater than those given by Carter, \iz., 

 20-6oooths and 3^-6oooths of an inch respectively. 



Yvesia commensalis, Whitelegge^ is possibly a. Stylostichon, 

 that is to say, the main skeleton consists of stout vertical' 

 columns composed solely of acanthostyles. The acanthostyles. 

 are, however, arranged plumosely, making an acute angle 

 with the direction of the fibres, and are not differentiated into 

 coring and echinating spicules. The dermal skeleton is a layer 

 of a closely packed isochelae arcuate, beyond which the outer 

 ends of divergent tufts of smooth oxea project slightly. The 



1 Dendy— Proc. Eoy. Soc. Vict., viii., 1896, p. 41; Carter— Ann. Mag. Nat.. 



Hist. (5). xvi., 1885, p. 352. 



2 Whitelegge— Austr. Mus. Mem., iv., 9, 1906, p. 433. 



