36 



ventral side almost flat, and the animal is nearly always somewhat broader than it is thick. 

 In the genus Homoeoscelis (pi. II and pi. XIII) as in Sphcer. curtipes (pi. X, fig. 2f and fig. 2g) 

 the body is much longer than it is broad, the length varying from V/3 to a little more than 

 twice the breadth; besides, mS. curtipes it is curved, so that, seen from the side, it presents 

 a moderately concave ventral outline. The length of the head varies between a little more 

 and a little less than half of the total length, in Sphcer. frontalis (pi. VII, 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 Sphcer. modesta (pi. IX, fig. 2f) the greatest breadth 

 lies before the middle of the maxillae ; 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 Sphcer. Bonnieri 

 (pi. VII, fig. 1 a), in S. frontalis (pi. VII, fig. 6 a) and in Mysidion abyssorum (pi. XII, fig. 2 e). 

 A distinct abdomen is found only in the genus Stenothocheres. Antennulae, antennae, rostrum, 

 maxillulae, maxillae 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 Sphcer. microcephala 

 and S. modesta, whose females lack both trunk-legs and caudal stylets, or only trunk-legs. 

 In Sphmr. 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 st} T lets. 



In the genus Stenothocheres the antennulae, the antennae, 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 maxillae, 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 

 maxillae, 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 ventral 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 Splicer, elegantula 

 (pi. II, 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 Sphcer. Calliopii (pi. Ill, fig. b h) the frontal margin is divided into 

 six lobes , in S. decorata (pi. VIII, fig. 3 f ) 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 



