34 
seen two such receptacula, but I cannot indicate their external orifices, as, strangely enough, 
I have never found spermatophores on any of the rather numerous specimens I have examined. 
ILL. Mysidion (pl. XI—X1I). The head is pretty well defined from the trunk, but 
so feebly chitinised in front and at the sides that the frontal and lateral borders are wanting. 
The antennule are much reduced and either 2-jointed or 1-jointed (pl. XII, fig. 2a, and 
fig. 1a, a). Antenne seem to be wanting. Mouth and maxillule as in Spheronella. The 
basal joint of the maxillze has at the inner edge one or two processes, and the appendage 
is a powerful prehensile organ. The basal joint of the maxillipeds has irregular outlines. 
Trunk-legs and caudal stylets are wanting. There is no genital area: the genital apertures 
are situated very far from each other (pl. XI, fig. 3b and fig. 3e); each of them has — besides 
the lips — its own skeleton, consisting of a list which is semi-circular or forms the larger 
part of a defective oval, the longest diameter of which runs parallel with the median line 
of the animal, and the opening of which is turned towards this line. The genital aperture 
is situated close to the posterior part of the list, and the muscles radiate towards its foremost 
part. The receptaculum seminis — odd, as far as I can see — is situated in the median 
line, far in front of the genital apertures (pl. XI, fig. 3e). The skin covering it is closely 
set with many — as many as twenty-six — spermatophores (s), and between them are seen 
stalks of other vanished spermatophores, some of these sticking together in bulks which 
cover the skin so completely that, in spite of several attempts, I have been unable to find 
the entrance or entrances to the receptaculum seminis. In fig. 3e the letter » marks recep- 
taculum seminis, which on each side opens into an obliquely backward running duct, which 
I have been able to follow towards the genital aperture (comp. the following genus). In 
Mysidion abyssorum I have found in the semi-circle surrounding the genital aperture a hole 
(or perhaps rather a spot, covered with a thin membrane pierced with small holes (pl. XII, 
fig. 2b, k) forming the outlet from a gland which I have found, though I have not been 
able to examine it more closely, and whose function is incomprehensible to me. — Several 
parts of the head of this animal are frequently covered with a viscous substance, by which 
it fastens itself to the marsupium of the host. This substance, in the females as well as in 
the males and the larve, is probably secreted by glands placed in front of the mouth (comp. 
the female of the following genus). 
TV. <Aspidoecia (pl. X11). This genus (one species) approaches very near to Mysidion. 
In this place only its most important characters will be mentioned, an exhaustive description 
being given in the special part of this work. The body is considerably broader than it is 
long, the head is distinctly defined from the trunk and pretty well chitinised, with rounded 
forehead and sides. The front is covered by a large adhesive plate (fig. 3d, s) by which 
the animal is attached, this plate at the same time covering the 1-jointed antennule (fig. 3h, a). 
Antenne are wanting; the maxillule are very small, without additional branch; the mouth 
is normal, but I have found no hairs along the mouth-border; the maxille are like those in 
Spheronella; maxillipeds are wanting. Trunk-legs and caudal stylets are wanting. Hach 
