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217
obvious, and it must accordingly be assumed, that Rathke, in describing the
animal under a new name, did not know the description given by Kr0yer. Of
course the specific name proposed by the latter author is that which should be
retained for the species. It is an easily recognizable form, though rather vari-
able in shape, according to the degree of distention of the marsupium. Also the
male is somewhat variable both as to size and in the shape of the metasome.
As is generally the case with parasitic Isopoda, the immature female exhibits
an appearance very different from that of the fully grown animal. In order to
show this difference and the successive transformations, several stages are figured
on PI. 91, and also figures of the embryo in its last stage, and of the larva in
the so-called cryptoniscian stage, are given on this plate.
Occurrence. This is by far the commonest of our indigenous Bopy-
rids, being met with rather frequently along the whole coast of Norway,
from the
Christiania Fjord to Vads0, infesting rather a large number of different Crusta-
ceans. I have found it on the following 6 species of the genus Spirontocaris
(Hippolyte): S. Gaimardii, polar is, puxiola, turgida, spinus, securifrons, and more-
over on 3 species of the genus Pandalus, viz., P. Montagu! , borealis, and pro-
pinqvus. It is also recorded by Dr. Hansen from Spirontocaris Phippsu and
by Sp. Bate from 8. Barleei, so that at present
it is known to occur on no less
than 11 different hosts. In all of them, the parasite occupies the very same place,
viz., beneath the anterior part of the metasome, more or less enclosed be-
tween the epimeral plates of the first 2 segments (see the uppermost figure in
PI. 90). On a closer examination, the parasite is always found to be firmly
attached by the aid of the one series of legs to the basal part of one of the
anterior pleopoda of its host, sometimes the right,
sometimes the left and
the distortion of the body to the one or the other side depends on this mode
of attachment. The male is found clinging to the ventral face of the metasome
of the -female, often occupying an oblique position and more or less concealed
by the protruding marsupium. In immature females the attached male is often
found to be still in the cryptoniscian stage, and I have also occasionally found
larval males of this description in different places on fully grown females. The
number of eggs and embryos contained in the marsupial cavity is immense,
and may amount to several thousand in all.
Distribution. British Isles (Sp. Bate), Kattegat (Meinert), Spitsbergen
(Norw. North Atl. Exp.), the Kara Sea (Hansen), Greenland (Kroyer), Grinnels
Land (Miers). Atlantic coast of North America (Harger).
28. Crustacea.