25 



near Ararat; and from the Grampians (Raff, 1912, p. 70). 

 Another species, Hypsimeto'pus intrusor^ Sayce^ occurs in the 

 burrows of the land crayfish, Engaeus cunwularms, in Tas- 

 mania (Sayce, 1902, p. 218). The remaining species of the 

 family appear to be genuinely aquatic, being found in surface 

 or underground fresh-water streams. 



Although the species under consideration is being placed 

 for the present under the genus Phreatoicus, it differs from 

 the other members of the genus in at least two characters. 

 The more evident of these, though not the more important, 

 is the greater expansion of the basal joints of the last three 

 pairs of peraeopoda, as shown in figs. 1 and 10. In the other 

 species of the genus these joints are comparatively narrow, 

 as in most Isopods(i); but in the present species the ex- 

 pansion is fully as great as that in most Amphipoda, and still 

 further increases theTesemblance to an Amphipod, caused from 

 the laterally compressed form of the body. It may be men- 

 tioned, however, that the next joint, the ischium, is com- 

 paratively long — longer than the succeeding joint, the merus — 

 while, as I have elsewhere pointed out (1894, p. 205), in 

 Amphipoda, with broadened basal joints, the ischium is 

 usually quite short. 



The other point of difference, though less evident, is of 

 more real importance, viz., the apparent absence of the coxal 

 joints of all the peraeopoda. In other species this coxal joint, 

 though small, is quite well marked and can be readily recog- 

 nized as the first joint of the limb, for it is not flattened 

 into a side plate or ''epimeron," as it is in most Amphipoda. 

 In P. latipes the pleura of the first four segments are pro- 

 duced downwards and outwards so as to hide the base of the 

 leg, and even when the attachment of the limb to the inner 

 side of the pleuron is examined, nothing is seen that can be 

 definitely recognized as the coxal joint. Consequently it must 

 either have become fused with the pleuron, but if so without 

 any suture or mark indicating its presence, or it is quite 

 absent. Caiman (1909, p. 202) has some interesting remarks 

 on the development of the coxal joint of the peraeopoda in 

 various Isopods, and gives examples in which it appears to 

 replace the pleural expansion of the segment, though, in 

 that case, it is marked off from the segment on the dorsal 

 surface by a distinct suture, except in the first segment, where 

 there is no suture, and in some of the Oniscoidea in which 

 the suture on the other segments also may disappear. 



(1) The basal joints are slightly broadened in Phreatoicus 

 australis. 



