20 G. 0. Sårs. 



both in front and behind in a rectangular corner. The egg- 

 ehamber proper is of circular form and contains, as a rule, 

 2 dark green ova, placed close together. 



The adult male (PI. I, fig. 6) is very small, not ex- 

 ceeding even a length of half a millimeter, and is at once re- 

 cognized from young females of the same size, by the great de- 

 velopment of the antennulæ, and by the structure of the 

 1st pair of legs. The shell also appears comparatively nar- 

 rower, and the rostral prominence is more produced. 



The antennulæ (PL II, fig. 12) are more than twice as 

 long as in the female, or about equal to half the length of 

 the body, and are, as a rule, extended straight downwards, 

 somewhat diverging to each side. The coarse lateral denticles 

 found in the female are wholly absent, whereas each antennula 

 carries anteriorly, at some distance from the tip, a slender 

 sensory bristle, of which no trace is found in the female. 



The 1st pair of legs (fig. 13) are each armed with a 

 strong anteriorly-curving hook issuing from the end of the 

 stem between the endopodite and exopodite, and terminating 

 in an obtuse point. 



The tail (fig. 14) does not differ much in shape from 

 that in the female. It is, however, somewhat shorter, and 

 has a small angular projection just in front of the caudal 

 claws, on which the seminal ducts debouch. 



Colour. — The body in both sexes is highly pellucid 

 and almost colourless. Only in large-sized females of the 

 parthenogenetic generations, it sometimes exhibits a more 

 or less distinct yellowish or olivaceous tinge. In such spe- 

 cimens, moreover, a small patch of a light brownish pig- 

 ment may rather frequently be found on each valve, 

 somewhat in front of the middle, especially observable in 

 the dorsal or ventral views of the animal (see PL I, figs. 1 & 2). 



