Marsh — North American Species of Diaptomus. 461 



The antennae reach slightly beyond the end of the furca. 

 The rii^ht antenna of the male is swollen anterior to the genic- 

 Tilating joint. The antepenultimate segment bears upon its 

 distal extremity a hook-like process which is rather less than 

 half the length of the penultimate segment. 



In the female fifth feet, the spines of the first basal segments 

 are very pronoimced. The second basal segments are armed 

 with rather delicate lateral hairs. The first segment of the 

 exopodite is stout. The second segment is of the usual form, 

 and the hook is denticulate on its inner margin. The third 

 segment is represented by two spines. The endopodite equals 

 in length the first segment of the exopodite, and is armed at 

 the tip with two spines and with short hairs. 



In the male fifth feet, the spines of the first basal segiuents 

 are very pronounced. The second basal segment of the right 

 foot is trapezoidal in form, and its length exceeds its average 

 width by about one-half. The lateral hair is at about one- 

 third of its length from the distal end. The first segment of 

 the right exopodite is about as broad as long, and has its distal 

 angle somewhat produced. The second segment of the exopo- 

 dite is elongate, being more than three times the length of the 

 first. The lateral spine is situated at about one-third the dis- 

 tance from the proximal end, is hook-shaped, and is inserted at 

 an angle with the plane of the segment — that is, it does not 

 lie in the same plane with the fiat surface of the segment. The 

 terminal hook is elongate, falciform, with a regular curvature. 

 The endopodite is short, rather less in length than the first seg- 

 ment of the exopodite, and is of a somewhat triangular form. 



The second basal segment of the left foot is similar in form 

 to the corresponding segment of the right foot, and is about 

 one-half as long. The lateral hair is situated well towards the 

 distal end. The first segment of the exopodite about equals 

 the basal segment in length, but is more slender. The second 

 segment is short, armed with a terminal pad, a pad on its in- 

 ner surface, and with two blunt spines near the distal end. 

 The pads are airnied with short, stiff hairs. The endopodite 

 is very slender and very nearly equals in length the two seg- 

 ments of the exopodite. 



