'54 



•ENDEAVOUR" SCIENTIFIC KE.SULT8. 



absent, for a short distance, from the distal extremity. 'J hese 

 spicules will be referred as the principal acanthostyles. The 

 acanthostyles of the second kind are the characteristic and 

 usually the sole elements of the dermal skeleton and at tiie 

 same time the predominant spicules of the ground substance. 

 From the evidence afforded chiefly by the \arieties pcrramosa 

 and di^ifaia — in which, owing to the absence of crowding, 

 the echinating spicules are, with greater ad\antage than in 

 the other varieties, individually discernible in detail — I am 

 convinced that spicules, similar in all respects to these dermal 

 acanthostyles, may also occur quite commonlv both as echin- 

 ating and coring spicules. Accordingl\-, I will not in general 

 use the terms "echinatiiis^'' and ''derumV to distinguish the 

 two forms of acanthostyles, but instead '"principal" and "ac- 

 cessory.'" One sees also in the different varieties that there 

 is a perfect gradation between the extremes of form shown 

 by the accessory spicules on the one hand and the principal 

 spicules on the other. Accordingly in determining the dimen- 

 sions of the accessory acanthostyles I haxe measured those 

 spicules only which are situated actually in the dermal skele- 

 ton, and as regards the principal acanthost\les, ha\e taken 

 account of their maximum size alone. The accessory acan- 

 thostyles are slightly cur\ed and slightly fusiform spicules 

 covered, almost or quite to the distal extremity, with .spines 

 which stand perpendicularly to the axis of the .spicule. The 

 isochelaj arcuatae are rather abundant and show a tendency, 

 which is strongly marked in some varieties, to become dif- 

 ferentiated into two sorts, a larger and a smaller. The 

 arrangement of the skeleton shows appreciable differences in 

 the different varieties, though not always to an extent that 

 permits of distinction in a verbal description. In the non- 

 encrusting varieties with the exception of levis, the fibres, 

 owing to their undulating courses and anastomoses, often 

 form a kind of pseudo-reticulation; in the variety perramosa, 

 actual transverse fibres in moderate number are developed. 

 This last-mentioned variety is therefore of considerable in- 

 terest, since it shows that a reticulate type of skeleton may be 

 developed directly from a dendritic type — a fact which lessens 

 the importance of a generic distinction based solely on such a 

 difference in the character of the skeleton. In all the varieties 

 the fibres are rich in spongin. The typical variety of the 

 species is Carter's KcJiiuonenia incntsfans from Port Phillip, 

 which has been described as "massive incrusting, thick, 

 covering the whole of a Pecten." I have not so far met with 

 any specimen in the .Australian Museum collection of Port 

 Phillip sponges which admits of identification with Carter's 

 species, but I ha\e before me two mounted sections prepared 

 bv Mr. W'hitelegge from pieces of British Museum specimens. 



