72 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



feet. The inuer ramas of the right fifth foot of the male is slender and 

 longer than in sanguineus; this is also true of the inner ramus of the 

 left foot. The terminal segment of the outer ramus is provided with 

 the same armature as sanguineus and also bears a ciliated plate along 

 its inner aspect. The terminal claw of the right leg is toothed. In 

 the female the inner ramus is more or less distinctly two jointed and 

 the claw of the outer ramus is toothed. Length of male 1.4 mm. 

 Color dark. In the long antenmB the species differs from sanguineus, 

 which it resembles in the armature of the last thoracic and first ab- 

 dominal segment. 



* Diaptomus arinatus Herrick. 

 Herrick '82 and 84; De Gaerne and Richard '89. 

 The form, which was indicated by only a few points, in the hope 

 that it might be subsequently rerecognized, has never again been seen. 

 It appears to be allied to sanguineus. The antenme are said to be 

 shorter than the body, the caudal stylets narrow, the right male an- 

 tenna has a hook upon its antepenultimate joint and is strongly gen- 

 iculate. But the one feature which may determine the species is the 

 existence of a tooth or spur near the base of the claw of the right fifth 

 foot of the male. 



* DiaiJtomiis oregronensis Lilljeborg. 



Plates IV, Figs. 7-12; IX, Fig. 3. 



De Guerne and Richard '89; Marsh '93. 



This species has been found only in Lake Miunetonka within the 

 limits of Minnesota, though Marsh speaks of it as occurring in Wis- 

 consin very generally in the smaller lakes. It was first found near 

 Portland, Oregon, by Trybom. 



The species is of medium size (1.5 mm. long) and rather graceful 

 habit. The antennae extend beyond the caudal stylets and are 

 strongly spined. The last two thoracic segments are confluent, and 

 bear one or two small spines laterally. The first segment of the ab- 

 domen is as long as the remainder and mucronate. The caudal stylets 

 are nearly twice as long as wide. The right male antenna is moder- 

 ately modified, its antepenultimate segment being unarmed. The 

 apical segment of the outer ramus of the fifth pair of feet in the female 

 is obsolescent with two sharp spines. The claw of the penultimate 

 segment is short and slightly curved; the inner rami are one-jointed 

 and armed with two large spines and fine bristles apically. The fifth 

 feet of the male are sub-equal, the terminal claw of the right foot being 

 geniculately curved and rather long. The accessory spine is near the 

 end of the preceding segment which also bears a small spine near the 

 middle. The inner ramus of the right foot reaches to the spine just 



