•200 



fully grown, the parasite causes a very large and conspicuous rounded tuber- 

 osity on the carapace of its host, occurring sometimes on the left, sometimes on 

 the right side (see fig. 24). The walls of this tuberosity fit exactly around the 

 sides of the parasite, and the very capacious marsupial pouch is thereby 

 completely closed, the incubatory plates extending only for some distance up the 

 sides of the cavity. As is the case with most other Epicarida, the parasite in- 

 variably turns its head backwards in relation to its host, and the dorsal face 

 towards the body of the latter. Such a position is in this instance of essential 

 significance for the aeration of the marsupial cavity, the water washing the 

 branchial cavity of the host from behind forwards being thus easily introduced 

 into the marsupium of the parasite from between the 1st pair of incubatory 

 plates. The number of ova contained in the marsupium is immense, and may 

 amount to several thousand in all. I have observed the embryo in its last stage 

 of development, immediately preceeding the 1st free larval stage, and have found 

 it to agree exactly with that of Phryxus abdomina.lis, as represented in PI. 91. 

 The male is found clinging to the ventral face of the metasome of the female, 

 just behind the last pair of incubatory plates, being generally placed trans- 

 versally to the axis of the female. 



Distribution. — Greenland (Kroyer), Barents Sea (Hoek), British Isles 

 (Sp. Bate). 



Gen. 3. PseudiOne, Kossman, 1881. 



S3'n. : Paloegyge, Giard & Bonn (part). 

 „ Phryxus, Sp. Bate & Westw. (part). 



Generic Characters. — Body of female oval or pyriform in outline, more 

 or less asmymetrical, with the segments both of mesosome and metasome very 

 sharply defined. Cephalon distinctly marginate in front. Segments of mesosome 

 with the lateral parts elevated and divided by a transverse groove into 2 lobes; 

 coxal plates well defined, though rather small, discontiguous. Epiineral plates 

 of metasome more or less projecting, lamellar ; last segment very small. Antennae 

 and oral parts as in Bopyroides. 1st pair of incubatory plates with the distal 

 segment produced to a narrow linguiform lobe, as in Bopyrus; the succeeding 

 pairs large, arching over the ventral face. Legs more or less projecting later- 

 ally, and of usual structure. Pleopoda well developed, biramous, rami lanceolate, 



