Mysidacea, Tanaidacea and Isopoda. 
421 
Genus Ichthyoxenus, Herklots. 
Ichthyoxenus japonensis, Richardson. 
/. japonensis, Richardson, 1913, p. 561, text figs. 4-6. 
Locality: — Lake Biwa, Japan, from Acheilognathus sp., February, 1915^ six 
females, five males (presented by Dr. T. Kawamura). 
Richardson's type specimens were taken from Acheilognathus cyonostigma (Jordan 
and Fowler) captured in Lake Biwa, and other specimens were found on various 
species of Acheilognathus and Gnathopogon from Lake Yago, Funayado, and Lake 
Biwa. The species is therefore fairly widely distributed in the freshwater systems 
of Japan. The present specimens are in agreement with Richardson's description 
and figures. 
Family SPHAEROMIDAE. 
Genus Exosphaeroma, Stebbing. 
Exosphaeroma oregonensis, Dana ? 
(PI. XVI, figs. 1-5.) 
E. oregonensis, Thielemann, 1910, p. 51, text figs. 41-47. 
Locality : — Whangpoo River, about 10 miles below Shanghai, 6-7 metres, 10. 
xii. 15, on bottom of hard mud, eight specimens up to 6 mm. (water fresh but 
tidal). 
Si Dong Ding, Tai Hu, China, 2^ metres, i. xii. 15, on muddy bottom with 
Potamogeton and other weeds, two specimens (fresh water). 
S.E. end of Si Dong Ding, Tai Hu, China, 3. xii. 15, on lower surface of stones, 
about 50 specimens (fresh water). 
I think this is the same species as that recorded from Japan by Thielemann 
(1910), but I am not so sure that it is Dana's species. Both this species and the 
following one have given me considerable trouble in their identification and I think 
it well to describe the appearance of the pleopods as they looked when dissected 
from spirit specimens, because it was mainly from this that I detected the presence 
of two species in this collection and also because the pleopods seem to me to 
depart from the descriptions of the pleopods of the Hemibranchiata as given by 
Han .sen. 
Pleopod 3 (PI. XVI, fig.' 3). Endopod with an opaque rather fleshy area on the 
inner proximal portion as indicated by the shading in my drawing. Otherwise both 
rami are transparent and I was not able to detect with certainty any regular bran- 
chial plications. Endopod with numerous plumose setae at the apex. Exopod two- 
jointed, distal joint edged with plumose setae all round, proximal joint without 
setae on the inner margin, but fringed with short setae on the outer edge. 
Pleopod 4 (PI. XVI, fig. 4). Endopod quite opaque and fieshy all over with two 
or three short plumose setae at the apex. Exopod two-jointed, inner proximal two- 
thirds, opaque and fleshy, rest transparent, a few short setae on outer edge of 
proximal joint, distal joint with a few (six or seven) plumose setae on its margins. 
Pleopod 5 (PI. XVI, fig. 5). Both rami thick and fleshy and opaque, exopod 
