202 
Nicholls — Tico New Phrcatoicids. 
tlie discovery of those well preserved Phrc^itoieid fossils from the 
Triusic beds of JS'.y.'VV. 
ill the possession of liliforin and relatively ioii| 3 ‘ lirst aiiteiinae, 
Nvphreatoicus is again in agreejneiit with A nipltiaopus and in sLrong 
contrast with FhrcatoicUi> and the group of subterranean genera; in 
this particulai', J\ capciisin is in agreement with the Australian and 
Tasmanian forms (witli tJie possible exception of 1\ apinosus) . 
A nearer approach to uniforniiTy in the length of the segments 
(^except the lirst free peraeon segnieiitj and, as a coiisecpieiice, the 
possession of a relatively long pleon telson region, must be accounted 
as a primitive character in Nopli rcaloicusA in ih spinusus, the 
development of this region is said to be even greater, being, according 
to Barnard p. no less tluin per cent, of the length 
of combined cephaloii and peraeon. in this latter species, liowever, 
there is a remarkable development of tlie terjninal teisonic projection, 
which, adds the eipiivalent of the length of a segment to this region. 
Generally in tlu‘ Bhreatoicidae the tend ncy is towards a reduction 
of the pleon region, a tendency which has become very pronounced 
in the Isopoda as a whole. in the members of this family, the 
pleon-telson region, expressed in terms of the percentage length of 
combined cephalon and peraeon, offers a series displaying increasing 
reduction. E. kershawi, 80Vc j E- tasmaniae and 1\ capensis, — 
7U%j B. jopneri, P. shepJiardi, P. kirkii, P. austyalis, P. assimUis, 
P. tppicus, in a bunch varying from 66V'' — 68 Vi, and iV kirkii var. 
dunedinensis to 4oVc. In the related subterranean genera an 
even greater reduction is attained, in Hyperoedesipus the figure is 
53Vc, in Hypsimetopus, 4:oVc, and in Phreatoicoides, '66%^ While 
agreeing with Chilton’s remarks (1906, p. 275) that measurements of 
this kind are not easily made with the same accuracy in all cases, 
and may vary to some extent in different individuals, I am of 
opinion, nevertheless, that such a series of stages in the reduction of 
the terminal body region as is found in the family is not without 
a. distinct significance. In a form living in surface waters, A. palus- 
tris, as I have stated above, Avliile the anterior peraeon appendages 
are largely functional in walking, aided (among <lebris), by the up- 
turned, backwardly directed and more elongate legs of the hinder 
series — for swimming the animal relies upon the pleopods with or 
Avithout the uropods, the deep pleura having a definite importance 
in this method of locomotion. In subterranean Tsopods, if one may 
Judge from llyperoede.^ipus and Cmregens, the animal creeps but does 
*In that generalised from Anaspides, the pleon-telson practically 
equals the cephaloii-peraeon in length; in Koonunga the xdemn- 
telson would appear to be a trifle the longer, the maxilliped 
segment here completely merged in the head. 
