194 
XmiOLLS — Tu'o Nnr Phrcafoicids. 
assimilis it is not i-onijilotoly tniiisvcTso ; in P. HhrpJiardi ami P. 
(yjiicii.s it is not tignired, nor is any refcn'eni-e made to its ])resence 
in P. kirhii. G. Hinith likewise makes no mention of it in his 
aeeount (1SU)9) of the Tasmanian species. In P. iypicus 1 should 
rather ex])ect it to have disa]p)eared, ])iit it will be surprising' if it 
])roves to be absent in the other species of Phrcato-icus. In all three 
species of A)iijiJiisopus it is certainly wanting', but, as Chilton has 
jKunted out (1891, j). Idd) a (piit(‘ similar groove is ])resent in many 
si)ecies of Idotca, and it is reasonable to sup])ose that it marks the 
suture Ixdween the first peraeon segment (the maxilliped segment) 
and the head, a segment fi'ee in the Anas])idacea, but incorporated 
in the head in Kooinuifpf and Iso])ods generally, all traces of its 
original anterior boundary having been lost in most of the members 
of this lntt(‘i‘ grou]). The first free sc'gment of the peraeon of 
PhrratolcKS is also hy way of reduction and incori)oration in the 
head, a condition which has actually come about in the Tanaidae. 
In the ])erjieon the coxal joints are greatly reduced and the 
antero-ventral corner of the several segments is distinctly produced 
in front or ]>erha])s is coming to lie external to the coxal joints. 
In the hinder series of h‘gs a postc'rior (d(‘ft only ])artly defines the 
Joint, which has become flattened (externally and incorporated with 
the ventral margin of its related segment. 
The ]deon segments are relatively deep and unnsually wide, the 
ventral l)orders almost and the posterior bordc'rs (piite free from 
I'etae. The fifth segment is dee])ly notched behind and is slightly 
shallower than the segment immediately in'eceding; the sixth, marked 
off from the telson only by a short suture running almost vertically 
upward from the ]>oint of origin of the uro]tod. It makes with the 
telson a large piece terminating (PI. XXIX, fig. 39) in a rounded 
]n'ojection which is not nj)turned as it is in most of the species 
of Phi'raloicufi. Its margin is entire and it is flanked laterally by 
a ]iaired projection bearing a stout terminal and a slighter lateral 
spine. Ventrally the margin of the telson bears on either side one 
large spine and a much smaller S])inule. 
A ppciidapfs. The (tirleniui (PI. XXVTI, fig. 18) is well 
develoiH'd, the i)eduncle scarcely differentiated from the flagellum; 
the basal joint is large, the second as long but more slender, the 
third shoi'ter, and little stouter than the ])r:nnixal article of the 
llagellum. The flagellum may have as many as sixteen joints, nearly 
oblong in outline and diminishing fairly regularly in length, the 
terminal joint, however, being a mere knob. Sensory setae (Fig. 
IS, s) occur on most joints, but the “olfactory setae” so clmracter- 
istic of Phreai<yU‘UH could not be recognised. 
The second antennae (PI. XXVII, fig. 19) are stout, of quite 
moderate length, Avith Avell defined peduncle (of a length approxi- 
