1096 Wisconsin Academy of Sciences, Arts, and Letters. 



the last abdominal segment, and at the other extreme the slender 

 form in which the furca may be three times as long as the last 

 abdominal segment. The form shown in the plate, (PL 

 LXXVIII, fig. 7) may be considered typical while the figure in 

 plate LXXVIII, fig. 6 is of the slender form. The outer mar- 

 gin of the f urea is bordered by a row of short spines. These are 

 not present in the male, and while always present in the female, 

 are very variable in size. It was noted by DeGuerne and 

 Richard ('92) that the specimens collected at Rufisque showed 

 these spines much less clearly than did the European speci- 

 mens. Brady (Brady 1906) also states that the serrulations 

 in the New Zealand specimens are less marked than in those 

 in Europe. There is much variability even in the same gen- 

 eral region. These short spines are commonly much more 

 prominent at the distal end of the furca. The lateral seta is 

 at the end of the furca. Of the terminal setae the outer is 

 short, sometimes spine-like, and, in the specimens with a short 

 furca, commonly stands at nearly right angles with the furca. 

 The second and third setae are prolonged ; the third is rather 

 less than twice as long as the second and only slightly exceeds 

 the combined length of the abdomen and furca. The fourth 

 seta is slender and weak, seldom much exceeding the first in 

 length, and sometimes is shorter. 



The first antennae are twelve-segmented and reach to the 

 third segment, or sometimes nearly to the fourth; their length 

 is quite variable. The last three segments (PI. LXXVIII, fig. 

 5) bear an inconspicuous hyaline membrane. Some of the 

 European authors say that these hyaline membranes are some- 

 times finely dentate, though commonly with entire margins. 

 This dentation has never been noticed in American specimens. 



The spinous armature of the terminal segment of the exopo- 

 dites of the swimming feet is 3, 4, 4, 3. 



The fifth foot (PL LXXVIII, fig. 8) is composed of a single- 

 segment. It is armed on its inner distal angle with a stout 

 spine with serrate edges, and on its outer distal angle with a 

 slender seta. Midway between these, on a prominent base is 

 a long slender seta, considerable exceeding in length the outer 

 seta. 



