Crustacean from Australia. 279 



that may be regarded as primitive is found in the first or coxal 

 segments of the thoracic legs. These are all of small size and, on 

 the last six segments at any rate, are movably articulated with the 

 body. In this character the Asellota resemble the Phreatoicidea, 

 but in other Isopods these segments are expanded into broad " coxal 

 plates" and more or less completely fused with the somites that 

 carry them. Finally, the last pair of abdominal appendages (uropods) 

 project from near the end of the body as bifurcate styles, like the 

 uropods of certain Asellota, and still more like those of Amphipods. 



In nearly all other respects — in the structure of antennules, 

 antennae, mouth-parts, thoracic legs, branchial abdominal limbs, and 

 even sexual appendages — the Phreatoicidea are commonplace Isopoda, 

 not differing essentially from many representatives of the central 

 and typical sub-order, the Flabellifera. That they retain certain 

 features which we believe to be primitive, or which point the way 

 to groups outside the order itself, has already been stated, but this 

 is true also of the Asellota and of the Flabellifera, and it is perhaps 

 impossible to rank any one of these three sub-orders as, on the 

 whole, more primitive than the others. 



Fig. 2. — Phreatoicus wianamattensis, Chilton. Eh8Btic(?). St. Peter's 

 Brickworks, Sydney, x SJ. (After Chilton.) 



The habitat and the geographical distribution of the Phreatoicidea 

 are also noteworthy. Isopods of truly freshwater habitat are few, 

 and in no other case are they conspicuously different in structure 

 from marine representatives of the group. "With the possible 

 exception of the single family Asellidse, they are scattered, and no 

 doubt recent, immigrants from the sea. The Phreatoicidea, on the 

 other hand, are not known to have any near relatives among the 

 marine Isopoda, and it is this that gives special significance to their 

 remarkable distribution in New Zealand, South-Eastern Australia, 

 Tasmania, and South Africa. 



In describing the first known species of Phreatoicus, Professor 

 Chilton stated that the group "must be of very considerable 

 antiquity". This prediction he has now had the good fortune to 

 verify in a striking manner. The specimens which he describes 

 were detected by Mr. R. J. Tillyard while investigating the fossil 

 insect fauna of Queensland and New South Wales, and were found 

 in the Wianamatta Shale of St. Peter's Brickworks, Newtown, 

 Sydney. The strata in which they occur were at first referred to 



