94 



BULUETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Female. — Head fused with the first segment; fifth segment pro- 

 duced laterally at the posterior corners and armed on either side with 

 two spines; genital segment widened anteriorly, with a prominent 

 spine near the center of each lateral margin; caudal rami fringed 

 with cilia on their inner margins; spines on first basipods of fifth 

 legs minute ; setae on second basipods as long as the basal segments 

 of the exopods ; hook on second exopod segment with a dentate inner 

 margin; third segment represented by two spines, the inner longer 

 than the outer; endopods about the same length as the basal seg- 

 ments of the exopods, each 

 tipped with two short spines. 

 Total length, 1.4-2.15 mm. 



Male. — Right first antenna 

 swollen, antepenultimate 

 segment with a stout re- 

 curved hook at its outer 

 distal corner; second basi- 

 pod of right fifth leg trape- 

 zoidal, its outer corner pro- 

 duced into a blunt spine; 

 second exopod segment 

 three times as long as the 

 first, the terminal claw den- 

 ticulate distally ; endopod 

 reaching the center of the 

 basal exopod segment; left 

 fifth leg only reaching the 

 tip of the right basipod, its rami subequal, the exopod tipped with 

 two curved processes, forming a sort of chela. Total length, 1-2 mm. 

 Remarks. — The little ice pond in which these specimens were 

 found is only 40 feet in diameter and is nothing but a stagnant pool, 

 very shallow during the summer and entirely filled with vegetation. 

 The species may be recognized by the color of the ovaries and ovi- 

 ducts, by the hook on the first antenna of the male, and by the 

 structure of the fifth legs in both sexes. 



DIAPTOMUS LEPTOPUS Forbes 



Figure 64 ; Plate 1, f 



Dlaptomus Teptopus Forbes, Amer. Nat., vol. 16, p. 646, pi. 8, figs. 17-19, 

 1SS2.— Maesh, Trans. Wisconsin Acad. Sci., vol. 15, p. 443, pi. 20, 1907. 



Occurrence. — Both sexes found in abundance in a small pond of 

 fresh water west of Edgartown on Marthas Vineyard. 



Distribution. — Mississippi Valley (Marsh) ; Minnesota (Herrick) ; 

 Colorado, Illinois (Forbes) ; Kentucky (Chambers) ; Woods Hole 

 (Forbes, M. and R. Rathbun). 



Figure G3. — Diaptomus sanguineus: a. Female, 

 fifth legs ; h, male, tip of right first antenna ; 

 c, male, fifth legs 



