138 TWELFTH ANNUAL REPORT. 



Sp. 2. Diaptomus saiig-iiineus, Forbes. 



(Plate Q. Fig. 12.) 



A species found with us in stagnating pools in early spring, 

 frequently following D. stagnalis and giving place to D. leptopus. 

 It prefers pools less foul than those affected by the latter, though 

 not rarely found with it temporarily. The species is quite variable, 

 and the variations are in directions suggestive of other species. 

 Measurements taken of specimens from a gathering from two 

 pools, one being more stagnant than the other, showed the follow- 

 ing results: — males from the less stagnant 1.7 mm.; males from the 

 other pool 2.0 mm.; a difference of 0.3 mm. (Males of D. stagnalis 

 from the latter gathering measured 3.4 mm., while the females of 

 that species vary between 3.8 — 3.9 mm.) Females measure about 

 1.8 mm. on an average, of which 1.3 mm. is the length of the thorax. 

 Such individuals have antennae 1.7 mm. long. The greatest width 

 is anterior to the middle, being about 0.5 mm. 



This species differs from D. stagnalis of which, in most respects, 



is a miniature, by the long antennae, short abdomen and 

 peculiar armature of the fifth feet. 



In the female the fifth foot is about 0.5 mm. long, and the outer 

 ramus has two small spines on the terminal joint, while the seg- 

 ment before the last has a powerful toothed claw. The inner ramus 

 is not evidently two-jointed. The first abdominal segment is 

 spurred on either side. The last thoracic segment extends into a 

 strong angle which bears a heavy spine terminally, and a smaller 

 spine dorsally. On the dorsal median line is a protuberance or 

 "hump'' on this segment. In the male the outer ramus of the right 

 foot of fifth pair is long, and terminates in a powerful curved, 

 toothed claw. The inner ramus is small and narrowed toward the 

 end; on the outside of the segment from which it springs is a blunt 

 spine, which is nearly as large as the ramus itself, and has been 

 mistaken for it. The left foot is very fleshy and its inner ramus 

 very rudimentar}^ The color is brilliant red or purple but variable. 

 Found in the southern states in autumn. 



Sp. 3. Diaptonius niinne tonka, (Sp. n.) 

 (Plate Q. Figs. 8—10.) 



A small species, smaller than either D. longicornis or D. sangui- 

 neus, was gathered in a pool bordering lake Minnetonka, which 

 contained also D. longicornis. It unites the chara3teristics of both 



