280 Notices of Memoirs — A Triassic Isopod Crustacean. 



the Trias-Jura, and Professor Chilton quotes Mr. Tillyard's opinion 

 that " evidence is accumulating that will probably place them in 

 the Upper Trias, probably as the nearest Australian equivalent of the 

 Rhsetic ". Dr. Smith Woodward, who has reported on the fossil 

 fishes from the same beds, agrees that tlie fish fauna, if it had been 

 found in the Northern Hemisphere, could not possiblj' have been 

 regarded as of later than Rhsetic age. 



The largest specimen obtained must have measured about 30 mm. 

 in length when complete. After examining a long series of 

 specimens, Professor Chilton shows that, in the general form and 

 segmentation of the body, the large size of the abdominal somites 

 with their downwardly directed side-plates, the size and shape of the 

 terminal segment and the uropods, the short antennse (or antennules), 

 and the form and proportions of the chief segments of the legs, the 

 fossils closely resemble the living Phreatoicidea. There is indeed 

 nothing to forbid their inclusion in the type-genus, to which he assigns 

 them under the name Phreatoicus ivianamatte^isis. 



It seems probable from the presence of insects, of such Mollusca 

 as Unio, and of numerous plant remains, that the beds in which the 

 fossils are found are of freshwater or estuarine origin, so that even as 

 early as the Triassic period the Phreatoicidea had adopted, or were 

 on tlie way to adopt, the freshwater habitat to which they are at the 

 present day confined. 



While Phreatoicus is thus one of the oldest, if not the very oldest, 

 of fossil Isopods yet discovered, and while it undoubtedly presents 

 certain primitive structural characters, it should be noted that it 

 throws no light on the phylogeny of the oi'der. It is, indeed, very 

 far from being an ancestral type, and it only emphasizes the fact that 

 the evolution of the group goes a very long M'ay back in geological 

 times. No doubt among these early Isopods, as among those now 

 living, a vast number of forms were two small and too delicate in 

 structure to be readily preserved as fossils, and, except for some 

 lucky chance, it is likely that we may never be able to trace, Avith 

 any clearness, the lines of evolution followed by the various 

 sub-orders. 



In reporting the discovery of a species of Phreatoicus living at the 

 Cape, Mr. K. H, Barnard called attention to its probable bearing on 

 the antiquity of the group and referred to th§ former extension of 

 " Gondwana land" over the areas where species of the genus now 

 occur. We now learn that they existed, probably as freshwater 

 animals, within the same area at a time when that extension may 

 have been still unbroken. Whether at that remote epoch their 

 geographical range was still wider, we cannot tell. If it was, then 

 it becomes a most extraordinary coincidence that their fossil remains 

 should first be found in a district where the living animals exist 

 to-day. 



