COPEPODA 



345 



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

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



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

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

 in male : Narragarisett 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.* 



13 



Fig. 542 Diagram ol 

 Cyclops (altered from 

 Siissw. 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- 

 racic 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- 



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 

 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. B. 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. 1067, 1909. "The Distribution of the Genus 

 Cyclops in the Vicinity of Haverford, Pennsylvania," by Reynold A. Spaeth, Proc. 

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



ment ; 

 furca. 



12, abdomen ; 1J 



