A FOSSIL ISOPOD OF THE FRESHWATER GENUS PHREATOICUS. 383 



still longer, reaching posteriorly to the hind margin of the 

 fourth pleon segment; basal joints of all rather widely 

 expanded, other joints longer than the corresponding ones 

 in anterior series; merus only slightly produced at postero- 

 distal angle. 



Total length of animal up to 30 mm. 



Occurrence. — Wianamatta Shale of the St. Peter's Brick- 

 works, Newtown, Sydney, New South Wales. 



Remarks, — For this species I have pleasure in adopting 

 the specific name " wianamattensis" which Mr. Tillyard 

 had assigned to it in his MS. To Mr. Tillyard belongs the 

 credit of being the first to recognise that the fossils were 

 the remains of a Phreatoicus. 



While the animal in general appears to come close to 

 P. australis, the terminal segment so far as it can be deter- 

 mined from the fossils appears to approach more nearly to 

 that of P. spinosus G. W. Smith, a species from Tasmania, 

 which is almost certainly identical with P. tasmanice Gr. M. 

 Thomson. In general appearance the fossil species also 

 comes very close to the South African species P. capensis 

 Barnard. 



4. Historical Account of the Fhreatoicidea. 



The Phreatoicidea form such a distinct and interesting 

 group of Isopoda that it is desirable to give the following 

 brief history of its members. 



The first species, P. typicus, a blind one, was described 

 by myself (1883, p. 89) from the subterranean waters of the 

 Canterbury Plains, New Zealand. For it I established the 

 genus Phreatoicus, and after discussing its relationships to 

 several of the main groups of the Isopoda I said (1883, p. 92): 



"The precise place of Phreatoicus in any system of classification 

 cannot as yet be indicated with certainty, but one thing is made 

 clear by the discussion, viz., that Phreatoicus, possessing as it does 



