54 On Sponges from South Australia. 



to that of the skeletal layer of the cavity which separates 

 them ; subcircular, presenting within respectively from one to 

 four or more openings which belong to the wall- structure, so 

 that each of these holes in the cloaca is the aperture of a 

 subcloacal dilatation or cavity. Structure of the wall like that of 

 H. com])ressa. Spicules of two kinds, viz. acerate and triradiate; 

 no quadriradiates : — 1, acerates of two forms, viz. one thin, 

 straight, cylindrical, fine, silky, and the other stout, fusiform, 

 and much curved, averaging 240 by 18-6000ths in. ; 2, triradi- 

 ates, viz. those of the surface, which are moderately large, 

 regular and irregular or sagittal, and those of the wall, which 

 are very large and long-shafted, averaging 120 by 6-6000ths 

 in., and the arms only a little less, so that this spicule 

 also is very nearly equiradiate. No. 1 in its thin form 

 is confined to the peristome, and in its stouter one echi- 

 nates the surface chiefly towards the mouth, where its outer 

 portion, which is the largest, is much curved, and the curve 

 directed towards the mouth, while the other or more attenuated 

 one is dee])ly sunk into tlie wall of this part ; no. 2, the tri- 

 radiates, in their smaller and more regular forms, are confined 

 to the sm-faces both of the outside of the specimen and the 

 cloacal cavity, while the larger and less regular ones are 

 confined to the interior of the wall, where their straight 

 long shafts, coming from opposite sides, overlap each 

 other, and their sagittal arms support the structure of the 

 surface and that of the cloaca respectively. No quadriradi- 

 ates or mortar-spicules were seen. Size of specimen, which 

 is compressed, 9-12tlis in. high by 5-12ths in. in its greatest 

 diameter. 



Ohs. I notice here, as in other instances, that the most 

 dilated spaces of tlie wall are under the surface and the cloaca 

 respectively, thus presenting suhdermal audi subcloacal c<i\ities. 

 The physiology of all this, and much more too, will by and 

 by have to be explained before the nature of the sponge is 

 fully elucidated. 



27. IIeteroj)ia spissa. 



Agglomerate. Specimen triangular, rounded, each angle 

 formed of the outer ])art of a conical individual connected 

 with a common centre ; growing upon a small branch of a 

 Fucus. Colour whitish yellow. Surface even, composed of 

 cribi'iform sarcode, fixing in a number of triradiates of diffe- 

 rent sizes, some of which are very large, and many with one 

 arm projecting beyond the common level, especially towards 

 the mouth. Pores consisting of the holes in the cribriform 

 sarcode, which for the most part are uniform in size, viz. 

 1 -830th in. in diameter, but here and there double this width. 



