206 
Nicholls — Two New Plireatoicids. 
The move io])Ust habit of Eophreatoicus links it ^vith the larger 
Tasmanian forms, ■with A wpliisopus, ami, also, with the still larger 
1\ wianamattoisis. Phrcaloicopsis eonld readily derive directly from 
the extinct form. 
yimpliisopus differs from Eophreafoieus principally in the 
loss of certain structures, notal)ly tlie scales, and the epipodite 
upon the second pleopod; in the develo])inent (or retention?) of 
cou])ling hooks upon first and second ])leo])ods, the structure of the 
penial filament, in tlie more complete degradation of the coxae of the 
peraeopods, in the absence of the sub-chelate condition of fourth 
])eracopod in the male, and the greater degree of expansion attained 
by the basos of the hinder legs. 
PJircafoicus, climbing from the plains to sub-alpine regions, has 
diminished in size, has retained into adult life the larval or juvenile 
condition of the first antennae. A less compressed peraeon and 
smaller tergites ])ermit of a greater exposure of the coxae, the palm 
has become restricted to the moi’e distal portion of the propod, the 
eyes have dwindled and disappeared, the expansion of the several 
joints of the peraeo])ods has undergone more or less retrogression, 
while the ]n-ehensile character of the fourth peraeo])od of the male 
has, perhaps, become more evident. A synchronous, or perhaps an 
earlier, (diange of hal)it may be supposed to have led to the modifica- 
tion of the burrowing forms, and thence to the occu])atioii of sub- 
terranean waters, a change which may reasonably be presumed to 
have come about independently at different times and places. 
In favour of the alternative view, that a form somewhat closely 
akin to P. typieus, but still ]) 0 ssessed of eyes, would more nearly 
]-esenible the ancestral condition, the following features in that 
species might be cited as primitive: — the large head, a first peraeon 
segment scarcely smaller* than the succeeding (well seen, too, in 
Hypsimetopus and Piircafoicoidcs, and less evident in Phreaioicopsis) , 
well developed coxae, basos rounded and without expansion, first 
maxilla with numerous plumose setae on inner lobe and still more 
numerous spines on outer lobe (erpially Avell seen in Phreaioicopsis) , 
]deon little compressed and without marked pleura, and terminal 
telsonic projection. Further, a shortened condition of the pleon 
appears to be of very general occurrence in the Isopoda and might 
reasonably be presumed to characterise the primitive Phreatoicid. 
Sub-al])ine forms surviving in widely scattered localities might well 
be extremely ancient (as the admittedly generalised Anaspidcs) and 
have given rise to newer forms in lowland country, stray specimens 
Avashing dorvn from high levels, the survivors undergoing modifica- 
tions in adaptation to their uoav conditions. The mountain forms 
*Tn P. capensis actually longer than the succeeding segment, 
