MarsJi — North American tipecies of Diaptomus. 413 



and concave on the inner margin. At about one-third of its 

 length is a small spine near the inner margin. The lateral 

 spine, situated at the beginning of the distal third of the seg- 

 ment, is slightly curved, and finely denticulate on the inner 

 margin. The terminal hook is slender, and equal in length to 

 the whole right foot. At slightly less than half its length there 

 is an abrupt angle. Distad of the angle, the inner margin of 

 the hook is denticulate. The endopodite is one-segmented, 

 rounded at tip, and equal in length to the first segment of the 

 exogodite. The left fifth foot of the male reaches a little be- 

 yond the middle of the second segment of the right exopodite. 

 The second basal segment is a little longer than wide, and some- 

 what shorter than the corresponding segment of the right foot. 

 The lateral hair is situated at the beginning of the distal third. 

 The first segment of the exopodite is about as long as wide, its 

 distal end considerably narrower than the proximal. The in- 

 ner margin is strongly convex and setose. The second segment 

 is about twice as long as the first, and is armed at the tip with 

 two finger-like processes; the outer of these processes is much 

 the larger, and is armed on its inner surface with a minute 

 setose pad. The inner process is separated from the main part 

 of the segment by a suture. The endopodite is slender, twice 

 as long as the first segment of the exopodite, and setose at the 

 tip. 



Length of female, 1.1395 mm. Length of male, 1.0248 mm. 



This species was found in collections made in connection with 

 the scientific work of the Michigan Fish Commission in Inter- 

 mediate lake, and in JSTorth lake on Beaver island. It also oc- 

 curred in a collection made by Dr. R. H. Ward in Crooked lake. 

 It was associated with D. oregonensis, to which it is closely re- 

 lated. It is apparently a rather narrowly localized species, for, 

 although collections have been made quite generally in the 

 Michigan and Wisconsin lakes, it has, so far, been found only 

 in these three localities. 



