l!OPEPODA 



345 



brandies of the second antennae of about the same length; 1 large dorsal 

 eye present; fifth pair of legs unirnmose: several species. 



T. setacaudatus Williams (Fig. 540). Length of female 1.4 mm.; 

 thorax of 5 segments; fifth pair of foet 2-jointed in female and 3-jointed 

 in male: Narragansett Bay; common. 



2. Labidocera Lubbock. Thorax of 4 segments; abdomen of female 

 of 2 or 3, of male of 5 segments ; first antennae of female of 23 segments ; 

 eyes present, a dorsal pair and a ventral median eye: about 14 species. 



L. sestiva Wheeler (Fig. 541). Length 2 

 mm.; body transparent; last thoracic segment 

 in male sometimes asymmetrical: Woods Hole; 

 common. 



3. ACARTIA Dana. First antennae of fe- 

 male 17-jointed, of uniform thickness through- 

 out; thorax of 4 segments; 1 large dorsal eye 

 present; abdomen of female of 3 segments; 

 outer branch of second antennae much shorter 

 than the inner; 18 species. 



A. tonsa Dana. Length 1.3 mm.; body 

 transparent : Atlantic and Pacific Oceans ; 

 often very common; a widely distributed 

 species. 



Family 4. CYCLOPIDAE.* 



Thorax with 4 free segments, first an- 

 tennae usually about two-thirds the length of 

 the body, both being modified in the male to 

 serve as prehensile organs; second antennae 

 short and uniramose; first four pairs of feet 

 biramous, outer branch 3-jointed, inner branch 

 1 to 3-jointed; fifth pair of feet rudimentary, 

 alike in both sexes, rudiments of a sixth pair 

 sometimes present; heart absent; 2 egg sacs 



Fig. 542 — Diagram ol 

 i'yclops (altered f r o ii; 

 Sussw. F. Deut.). 1, first 

 antenna ; 2, second anten- 

 na ; 3, mandibles ; 4, first 

 maxilla; 5, second maxilla 

 (maxilliped) ; 6, 7, 8, 9, 

 the first four pairs of tho- 

 i-acic legs, each leg being 

 composed of a basal piece, 

 the protopodite, and two 

 terminal pieces, the exopo- 

 dite and endopodite : 10, the 

 fifth pair of thoracic legs ; 

 11, receptaculum seminis, 

 in the first abdominal seg- 

 ment ; 12, abdomen ; 13, 

 furca. 



present : about 75 species and 5 genera, mostly 

 in fresh water. 



1. CYCLOPSf 0. F. Miiller (Fig. 542). Thorax with 4 free segments, 

 abdomen with 5 segments in the male and 4 in the female ; first antennae 



* See "A Contribution to a Knowledge of North Am. Fresh-Water Cyclopidae," by 

 E. C. Forbes, Bull. 111. St. Lab., Vol. 5, 1897. 



t See "A Revision of the North American Species of Cyclops," by C. D. Marsh. 

 Trans. Wis. Acad. Sci., Vol. 16, p. 1007, 1000. "The Distribution" of th*i(4euus 

 Cyclops in the Vicinity of Haverford, Pennsylvania," by Reynold A. SpaetV'^roc. 

 Acad. Nat. Sci., Vol. 66, p. 20, 1914. 



