274 Mr. H. J. Carter on 



epithelium covering the interstices. Vents not seen. Struc- 

 ture generally compact, and tlie parts mentioned in H. austra- 

 liensis so indistinctly and delicately developed that, although 

 evident, I have not been able to make a vertical section in 

 which the forms of the ampuUaceous sacs could be satisfactorily 

 seen; still the form, if not identical, appears to be but a 

 variety of H. australiensis, chiefly dependent on its habit for 

 its differences. The " creno-tuberculated " state may be an 

 exaggerated form of the puckerings on the surface of this kind 

 of sponge generally. 



Halisarca 7'eticulata. 



Enveloping with a thin layer the calcareous fronds of 

 Reteporian and Escharidian Polyzoa, uniting through the 

 interstices of the former ; varying in thickness under 3-24ths 

 in. Consistence exceedingly tough. Colour whitish grey. 

 Surface smooth, presenting a tough fibro-reticulated structure, 

 with more or less round interstices, covered by a thin epi- 

 thelial layer. Pores in the interstices. Vents here and there 

 indicated in their position by the centres respectively of sub- 

 stellate, branching, superficial, excretory canal-systems in the 

 form of venations, which are seen just below the epithelium. 

 Structure essentially fibrillous throughout, commencing (in 

 the vertical section) with the thin epithelial layer, followed by 

 the fibro-reticulated one, whose tough fibrilla3 extending 

 inwards are accompanied by the usual subglobular form of 

 ampuUaceous sacs, succeeded in one specimen by the develop- 

 ment of small ova, each furnished with a germinal vesicle and 

 its nucleolus or germinal spot, and about 8-6000ths in. in 

 diameter. These are situated in juxtaposition in the midst of 

 a tough fibrillous trama, but each separate and provided with 

 a cell-cavity, which, on being scratched out from the general 

 mass, comes away with the ovum inside it, while the surface 

 of the " cell-cavity " is fringed with filaments which appear 

 to have been in connexion with the fibrilla3 of the trama. 

 Size of specimen indefinite, following that of the fronds of the 

 Polyzoon on which it may be growing. There are three 

 large specimens of this species, viz. one from " Port Phillip 

 Heads" and the other two from " Port Western," all growing 

 on the same kind of Polyzoa, and all presenting the same 

 characters, which, from the strongly marked and tough reti- 

 forra fibre-structure of the surface, has been designated 

 " reticulata^ It is totally different from either of the fore- 

 going forms in this respect and from every other species of 

 this order that I have seen, so that I am in doubt whether it 



