100 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



stable; Mashpee Pond, Mashpee; Flax Pond, Falmouth; Browns 

 Pond, Falmouth; Sidleys Pond, Falmouth; Salt Pond, Falmouth. 



Distribution. — Oregon (Lilljeborg) ; Wisconsin, Michigan (Marsh) ; 

 Minnesota (Herrick) ; Iowa, Illinois, Indiana (Schacht) ; Northwest 

 Territories (Marsh) ; eastern Massachusetts (Pearse) ; Great Lakes 

 (Marsh) ; Ontario, New Brunswick (Klugh). 



Color. — Body clear and as transparent as glass, except around the 

 mouth ; here in some individuals there was a faint wash of red ; again 

 the red formed a narrow circle, or a small patch, and rarely covered 

 much of the ventral surface of the head; eye ruby red, the lenses 

 scintillating like diamonds ; in other specimens the ventral patch was 

 blue next to the mouth, and outside of this brownish or reddish; 

 ovaries, oviducts, and eggs pale olive-green. 



Figure 67. — Diaptomus oregonensis: a. Female, dorsal, showing number and 

 arrangement of eggs in single egg-case ; i, female, flftli leg ; c, male, 

 fifth legs ; d, joung male, fifth legs ; e, young female, fifth legs ; f, 

 female, ventral view of urosome 



Female. — Metasome very slender; posterior corners of fifth seg- 

 ment short, each with a single spine; genital segment enlarged 

 anteriorly, with a minute spine on each lateral margin at the center 

 of the enlargement; spines on first basipods of fifth legs minute; 

 setae on second basipods three-fourths as long as first exopod seg- 

 ment; hook on second exopod segment acuminate and fringed with 

 cilia on the inner margin; endopods 1-segmented, longer than the 

 first exopod segment, with two equal apical setae and an inner 

 process. Total length, 1.25-1.5 mm. 



Male- — Posterior corners of fifth segment rounded, without spines ; 

 second basipods of fifth legs longer than wide; endopod of right 

 fifth leg reaching middle of second exopod segment and unarmed; 

 first exopod segment wider than long, second segment twice as long 



