A FOSSIL ISOPOD OF THE FRESHWATER GENUS PHREATOICUS. 375 



the whole of the pleon is present, and, although parts of it 

 are indistinct, the conical terminal segment is clearly 

 marked, and shows a regular projection at the posterior 

 end as indicated in the figure. This appears to have the 

 upper and lower sides nearly similar and evenly curved 

 into the general outline of the segment, so that the actual 

 projection is not marked off by a depression at its base, as 

 in P. australis and others of the existing species. It 

 appears to resemble most nearly the terminal segment of 

 P. tasmanice G. M. Thomson and P. spinosus G. W. Smith ; 

 these two, however, being probably identical. The existence 

 of this terminal segment was not observed until I had 

 already become quite confident that the other impressions 

 were those of a Phreatoicus, and the possession of this 

 characteristic terminal portion of the pleon fully confirms 

 the correctness of that decision. 



The segments 1, 2, 3, 4 and 5 of the pleon are fairly 

 distinctly marked so far as their inferior margins are con- 

 cerned, and the general line of their dorsal surface is also 

 clear, though the upper lateral portion of the fourth and 

 fifth segments has been broken away. At the infero- 

 posterior angle of the fifth segment there is an indication 

 of an appendage which possibly represents the uropod, but 

 this is not distinct enough to make out anything of its 

 special structure. 



The depth of the pleon segments in the specimen is 

 about 5 mm.; the peraeon segments are hardly sufficiently 

 marked to admit of accurate measurement. 



Specimen 6, Fig. 6. (Block 236). 



In this impression the posterior and dorsal portions of : the 

 pleon are absent, though the lower portions of segments 1, 

 2, 3 and 4 can be distinctly identified, and the whole of^the 

 peraeon and apparently the head are also present, although 

 much confused and difficult to make out. 



