738 



FRESH-WATER BIOLOGY 



247 (120) No eye; ocellus only Monospilus Sars 1861. 



Sole species Monospilus dispar Sars 1861. 



Form oval or round. Shell not cast in molting, as in 

 Ilyocryptus. Valves nearly round with fine setae along 

 ventral edge. Head very small, depressed, movable. 

 Keel of labrum with about 4 scallops on ventral edge. 

 Post-abdomen broad, short, with about 5-7 marginal 

 denticles and numerous clusters of fine hairs. Eye lack- 

 ing; ocellus large. Antennules short, not reaching apex 

 of rostrum. $ with hook on first foot; post-abdomen 

 tapering, triangular, somewhat resembling that of Grap- 

 toleberis. Color brown-yellow. Length, 9 1 ca. 0.5 mm.; 

 $ , ca. 0.4 mm. 



New England, Wisconsin, Minnesota; rare. 



Fig. 1168. Monospilus dispar. 



0.r MM. 



248 (i) Body and feet not covered by shell. Feet subcylindrical or flattened, 

 jointed, prehensile. . . Section B. Gymnomera . . 249 



No fornices. Rami of antennae 3- to 4-joiuted. Feet, 4 to 6 pairs, jointed, prehensile. 



249 (250) Four pairs of feet, stout, compressed, with claw-Kke spines and 

 branchial appendages. 



Tribe I. Onychopoda. 

 Sole family. . Polyphemidae Baird. 



Body very short. Shell converted into large globular brood-sac. Caudal process long, 

 slender, with 2 long caudal stylets or setae. Rami of antennae with 3 and 4 joints. Eye very 

 large; no ocellus. Labrum large. Two small hepatic ceca. 



One genus Po/y^/jewMj O. F. Miiller 1785. 



Sole species Polyphemus pediculus (Linne) 1761. 



Brood-sac globular, with 

 20-2S young in full grown 

 spedmens. Antennules 

 very small, on ventral sur- 

 face of head. Head large, 

 filled in front by huge 

 movable eye. Antennae 

 with 7 setae on each ramus. 

 Feet stout, with strong 

 daws, and branchial ap- 

 pendage; fourth pair, very 

 small. Length, 9. meas- 

 ured to back of brood-sac, 

 to 1.5 mm.; $ , 0.8 mm. 



Common in northern 

 United States in lakes, 

 pools, and marshes. 



FIG. 1169. Polyphemus pedio- 

 ulus. 



