154 Trans. Acad. Sci. of St. Louis. 



but I have frequently found the latter in places where 

 the former was not in evidence. 



The temperature of the water in which it was found 

 varied from 4° to 12° C. 



The females varied much in color. From some localities, the specimens 

 were blood red all over, except dark streaks due to eggs in the brood- 

 sac; from other localities, the thorax was bright blue tinged with yel- 

 low, through which shone the orange to brown digestive tract, the distal 

 half of the abdomen was orange, the antennae were reddish brown, and 

 the legs a deep blue; from another locality the body was straw color, 

 with a dash of red on the antennae and a portion of the thorax, while 

 the legs were almost black. With one exception, the males encountered 

 were all bright red. The exception was a pale, pink male found among 

 a large number of males of the typical color. This was probably a case 

 of albinism. 



The dimensions of the females are given in table IV. The following 

 dimensions of the male are averages derived from measurements of 

 twenty-five individuals. Length of the thorax 2.13 mm., length of the 

 abdomen 1.04 mm., length of the abdominal furca 0.14 mm., length of 

 the abdominal setae 0.70 mm., total length, excluding the abdominal 

 setae, 3.17 mm., total length, including the abdominal setae, 3.87 mm. 



Associated with it, in addition to the Entomostraca 

 mentioned in table I., were : Brancippi, Assellidae, gam- 

 marids, water-boatmen, diving beetles, hydrachnids, pla- 

 narians, Limnaeus, and Hydra fusca. 



3. Diaptomus augustaensis, n. sp. 



PI. XXXVI. f. 1-4. 



This is a small, slender species closely related to D. 

 ashmedi. 



Female. — Thorax long and slender, almost three times as long as 

 wide: suture between the head and thorax distinct in fresh specimens; 

 but indistinct on the dorsal aspect of specimens mounted in balsam. 

 The last two thoracic segments distinct, the last strongly bifid; each arm 

 of the bifurcation broad and slightly concave on the posterior margin, 

 with the two posterior angles terminating in a sharp spine or tooth. 



The abdomen is slender; including the furca, it is not half so long 

 as the cephalothorax. The first abdominal somite, which is about as 

 long as the remainder of the abdomen, including the furcal rami, is 

 dilated laterally and armed on each side with a prominent spine; the 

 second segment is slightly shorter than the third; the furcal rami are 

 about twice as long as wide. 



The 25-jointed antennae reach about to the base of the furcal rami. 

 On the fifth foot, the basal joint bears, at its outer angle, a small spine; 



