36 
ventral side almost flat, and the animal is nearly always somewhat broader than it is thick. 
In the genus Homoeoscelis (pl. IL and pl. XIII) as in Spher. curtipes (pl. X, fig. 2f and fig. 22) 
the body is much longer than it is broad, the length varying from 1°/s to a little more than 
twice the breadth: besides, in S. curtipes it is curved, so that, seen from the side, it presents 
a moderately concave ventra) outline. The length of the head varies between a little more 
and a little less than half of the total length, in Spher. frontalis (pl. VIL, fig. 6a—6b) it does 
not take up a third part. The body is usually broadest somewhat behind or almost on a 
line with the base of the maxillipeds. In Spher. modesta (pl. LX, fig. 2f) the greatest breadth 
lies before the middle of the maxilla; in several species it is rather far behind the head, 
and in this case the trunk is somewhat or much larger than the head, viz. in Spher. Bonniert 
(pl. VIL, fig. 1a), in S. fronfalis (pl. VIL, fig. 6a) and in Mysidion abyssorum (pl. XII, fig. 2e). 
A distinct abdomen is found only in the genus Sfenothocheres. Antennule, antenna, rostrum, 
maxillule, maxilla and maxillipeds are much like those of the female, still we find a number 
of minor differences which must be mentioned. Trunk-legs and caudal stylets are well 
developed in all the species whose females possess these organs, though as a rule they differ 
very much in the two sexes, and they are also found in a few species, as Spher. microcephala 
and S. modesta, whose females lack both trunk-legs and caudal stylets, or only trunk-legs. 
In Spher. dispar, S. insignis, S. marginata, as well as in the genera Mysidion and Aspidoecia, 
the males have not the slightest rudiment either of trunk-legs or of caudal stylets. 
In the genus Stenothocheres the antennule, the antenne, the rostrum and the mouth- 
appendages are situated on the foremost rather flatly vaulted part of the ventral side of the 
body. In all the other genera the surrounding of the rostrum and the mouth-appendages in 
front and at the sides lie more or less deep and are limited anteriorly by an outstanding 
border, which is frequently rather high or forms a slanting plate, at the sides by very 
conspicuous lateral borders, which usually run nearly parallel from the front towards the 
base of the maxilla, whence they curve more or less outward towards the lateral margins 
of the animal and vanish somewhat behind the base of the maxillipeds. The shape of these 
lateral borders is rather variable and difficult to describe, but the numerous illustrations 
will show two outstanding rounded plates bending like a cape towards the base of the 
maxilla, and outside these protruding borders we can always see something of the slanting 
lateral surfaces of the head, when looking at the animal from the yentral side. The frontal 
border is sometimes distinctly separated from the lateral ones, but it usually forms a direct 
or nearly direct continuation of them; in most forms it is evenly curved; in Spher. elegantula 
(pl. LL. fig. 2f) and in kindred species it has a deep incision on each side, by which the 
frontal plate is divided into a large, median, almost square part and two much smaller 
rounded lateral lobes. In Spher. Calliopii (pl. II, fig. 5h) the frontal margin is divided into 
six lobes, in S. decorata (pl. VUII, fig. 3f) the frontal plate is much elongated, with the 
anterior end cut off transversely and with several incisions, one in the middle and two on 
each side, by which it is divided into four square and two low triangular lobes, all of which 
