METRIDIA. 43 



what leaflike and minutely serrated on the outer edge. 

 Fifth pair of feet cylindrical, unbranched, in the male 

 four- and in the female three-jointed ; those of the 

 female, however, much shorter than of the male, and 

 having joints of nearly equal length {fig. 10) ter- 

 minated by two or three fine short setae. In the male 

 the first and fourth joints are much elongated (figs. 

 8 and 9), and the second joint bears a slender curved 

 process ; the foot of one side is also much more 

 slender than that of the other. The inner branch of the 

 second pair of feet in the male has the first joint very 

 much excavated at the upper and inner margin, the 

 lower margin of the excavation having alarge and strong 

 spine (PI. LVI, fig. 20 b) at the angle, and two smaller 

 ones internally. Abdomen of female 3-, of male 5- 

 jointed. Caudal setse short, scarcely half the length 

 of the abdomen (fig. 11). Length, exclusive of the 

 caudal setse,* ^th of an inch (1*6 mm.). Arctic 

 examples belonging apparently to this species, taken 

 during the expedition of the "Alert" and "Discovery," 

 and now in Mr. Norman's possession, are much larger, 

 measuring at least twice as much (yth of an inch). 



I am indebted to my friend Mr. E. C. Davison, R.N., 

 of Sunderland, for several collections of Entomostraca 

 taken in the tow-net off Ireland and in other localities, 

 and my knowledge of the present species is almost 

 entirely derived from these gatherings, in several of 

 which it occurred plentifully. The localities are as 

 follows, — off the mouth of the Shannon ; Galway Bay ; 



* Except where otherwise stated, the measurements of length are in 

 all cases to be taken as exclusive of the tail setse. 



