186 
Antenne wanting. Mouth middle-sized; mouth-border provided with very distinct hairs. 
Maxillule small, probably constructed like those of the female, and without additional branch. 
Maxille extremely large, the basal joint much compressed and very broad; the two last 
joints, which are entirely fused, form a long and powerful, proximally somewhat curved, 
distally almost straight joint. The basal joint of the maxillipeds somewhat smaller than in 
most species of Spheronella, second and third joints fused into one exceedingly short joint, 
which has no spine at its distal inner angle; last joint slender, pointed, perceptibly longer 
than the penultimate one. The sub-median skeleton without processes on its posterior part. 
The trunk without legs and caudal stylets. (Fig.3k only shows one single, but exceptionally 
large spermatotheca (q), but this no doubt is an anomaly in the specimen illustrated, 
as in two other individuals I found, as usual, two much smaller and normally situated 
spermatothece. 
OVISACS. They are hinged to the lists of the genital apertures, sub-globular or 
shortly pyriform, from scarcely middle-sized to small; their number can amount to thirteen 
or fourteen. Eggs of average size, not numerous. 
LARVA. Resembles in nearly all its features (fig.3m) the larve of certain Species 
of Spheronella parasitic on Amphipoda. The essential differences found are as follows: the 
second joint of the maxille is short and comparatively thick (fig. 3n), the third joint is 
finely serrated at its inner margin; the seta of the caudal stylets is short, not half the 
length of the cephalothorax. 
POST-LARVAL DEVELOPMENT. The male comes out of the larva (fig. 3m) 
directly, without any intermediate stage. Whether the female passes through the pupa stage 
is not known, but it appears more probable to me that its development resembles that 
of the male. 
HABITAT. The females live attached to the eye-stalks, the carapace, the back 
and sides of the free thoracic segment and the six first abdominal segments of all species 
of the genus Hrythrops G.O. Sars (order Mysidacea), in Norway. 
REMARKS. The genus comes very near to Mysidion, and the characters by 
which both genera are distinguished from those previously described are stated in the 
remarks about the last-mentioned genus. From the latter the female differs in the lack of 
maxillipeds, in the tolerably short distance between the genital apertures, in the ring by which 
each of these apertures is surrounded, and by the two conspicuous chitinous knots above 
the receptaculum seminis. The male deviates both from Mysidion and from all other genera 
in the minute size of the antennule and in the smallness of the distal part of the maxillipeds. 
And this genus deviates from all other forms by living attached to the outside of the free 
surface of its hosts. — The whole of my large material collected by Prof. G. O. Sars I have 
referred to one species; the subsequent remarks about this parasite will form a supplement 
to the above account of the type. 
