Sponges from South Australia. 273 



Taking tliem separately, then, they may be distinguished 

 thus : — 



Halisarca australiensis. 



Massive, cuboidal or plano-convex, spreading, growing over 

 the detritus of the sea-bed of the locality (agglomerated sand 

 and shells) , or miattached and free ; following no particular 

 shape, but generally more or less round and lobed. Consist- 

 ence doughy. Colour grey or brown. Surface very smooth, 

 puckered here and there, presenting under the microscope a 

 thin layer of small epithelial cells, covering a soft fibro-reticu- 

 lated structure, whose interstices represent the subdermal 

 cavities. Pores in the epithelial layer over the interstices. 

 Vents single, here and there on the smooth parts and in the 

 puckered depressions respectively. Structure (as seen in the 

 vertical section) commencing from the outside with the thin 

 layer of epithelium, followed by the soft reticulated structure, 

 into whose interstices the pores open, and then the body- 

 substance, more or less traversed by lacunse and the canals of 

 the excretory systems, whose forms, whether vertical and 

 crevice-like or oblique and transverse, are influenced by the 

 line of section, surrounded more or less radiatingly by aggre- 

 gations of ampullaceous sacs, which are subglobular or pyri- 

 form. Size of specimens, of which there are several, as 

 variable as their form, but not more than 2 inches in their 

 longest diameter. 



Obs. It will therefore be observed that the plan of structure 

 is the same as that of all other sponges. How the particles 

 of nourishment which pass in with the water through the pores 

 are subsequently conveyed to the ampullaceous sacs remains 

 to be shown. 



Halisarca ascidiarum. 



Incrusting, growing over the surface of sessile as well as 

 stalked Ascidians, more especially over Boltenia^ seldom more 

 than l-12th in. in thickness, and presenting a creno-tubercu- 

 lated or mesenteric form of surface corresponding to that of 

 the subjacent cartilaginous test, but not of the stem, where 

 it is even still more creno-tuberculated, while the stem 

 remains smooth, so that it is probably the form assumed by 

 the Halisarca itself. Consistence yielding, like that of soft 

 dough. Colour pinkish or brownish white. Surface very smooth, 

 presenting under the microscope a thin layer of small epithe- 

 lial cells, covering a soft homogeneous fibro-reticulation, whose 

 interstices represent the subdermal cavities. Pores in the 



