Sponges ft'om South Australia. 139 



superficially by the presence of a dermal layer of small acerates 

 and mortar-spicules. Pores indiscriminately scattered over 

 the surface. Vent single, at one end of the transversely elon- 

 gated head, which is more acuminated than the other, wliere 

 it is furnished with a short glistening peristome, leading into 

 a cloaca that extends in a cylindrical form, increasing in size 

 from the base to the head, where, corresponding with the 

 hammer-like form of this part, it divides into two portions, 

 one of which leads to the closed, and the other to the open 

 end ; surface of the cloaca presenting throughout several sub- 

 circular holes of different sizes and distances apart, each of 

 which is furnished with a sphinctral diaphragm of sarcode, 

 and the whole sparsely echinated with the fourth arms of 

 quadriradiates, which are very short. Wall composed of can- 

 cellated canaliferous sarcode, like that of the genus Heteropia, 

 traversed in its entireti/ longitudinally and abundantly by 

 the large acerate spicules at various distances apart, which 

 are crossed perpendicularly at intervals by bundles of small 

 thin tricurvates which possess the peculiar form that will be 

 mentioned hereafter, and extend from the surface on one 

 side to the cloaca on the other. Spicules of three kinds, viz. 

 acerate, triradiate, and quadriradiate : — 1, acerates, consisting 

 of those which belong- to the peristome, the body, and the 

 surface respectively ; 2, triradiates, divided into those which 

 belong to the surface and the cloaca respectively • and 3, 

 quadriradiates, which appear to be very few in number on the 

 cloaca, confined to the surface of the latter and that of the 

 body. Acerate of the peristome long, straight, cylindrical, 

 thin, glistening, sharp-pointed at each end, averaging 300 by 

 l^-GOOOth in.; that of the body, including the wall and the 

 surface or cortex, also long but thick, almost equally fusiform, 

 slightly curved and more or less sharp-pointed at each end, 

 averaging 330 by 18-6000ths in., and that of the surface 

 minute, straight, and lance-pointed at one end, in short the 

 " mortar-spicule;" all three forms equally abundant in their 

 several localities. Triradiates of various forms and sizes, 

 according to their position, viz. those on the surface small 

 and those in the cloaca large, the latter sagittal with very long 

 and almost straight arms expanded perpendicularly to the 

 shaft, which is very short and straight, apparently reduced in 

 size inversely to that of the arms, the latter hecommg Jiattened 

 vertically towards the commencement or proximal end of the 

 peristome, where, by extending perpendicularly across its 

 spicules while the reduced shaft is directed as perpendicularly 

 backwards, they act, as before stated, in securing the position 

 of this palisading like the cross bars of a row of pales. Quadri- 



