332 



CRUSTACEA 



eyes sessile and close together; first antennae minute, second large, with 

 2 terminal branches; 18 to 28 pairs of broad feet, the first or the first 

 and second pairs being prehensile in the male: in fresh water, differing 

 from the Cladocera and Ostracoda in being much larger and in having 

 distinct segmentation and more appendages and an abdomen which is not 

 bent under the thorax; about 5 genera. 



Key to the genera of Limnadiidae here described : 



Ci Lines of growth on shell ; 24 pairs of feet 1. Cyzicus 



a^ No lines of growth ; 10 to 12 pairs of feet 2. Limnetis 



1. Cyzicus Audouin {Esthe- 

 ria Riippell). Shell oval and 

 opaque, amber-colored ; body 

 rather thick; head with a long 

 narrow rostrum; about 24 pairs 

 of flat feet, the first two pairs 

 being prehensile in the male: 

 numerous species, about 8 in 

 America, all in the West. 



C. morsei (Packard) (Fig. 

 512). Shell 12 mm. long, 8 mm. 



high, and 6 mm. across; the two branches of second antennae with 17 



and 16 joints each: widely distributed throughout 



the central and western parts of the country. 



2. Limnetis Loven. Shell oval or spherical, with 



no lines of growth ; head with a large rostrum ; 11 or 



12 pairs of feet, the first pair being prehensile in the 



male; eggs carried in a dorsal brood chamber: 4 



species in America. 



L. gouldi Baird (Fig. 513). Body rather thick; 



second antennae with 16 segments in each branch; 



length of shell 3 mm.; breadth 2.5 mm.; color pink; eyes black: eastern 



and central America, westward to the Mississippi. 



Fig. 512 — Cysicus morsei (Packard), 



Fig. rtlP, — Limnetis 

 (jouldi (Packard). 



Suborder 2. CLADOCERA.* 



Water fleas. Body usually short and compact, without segmenta- 

 tion, and enclosed in a bivalve carapace; 4 to 6 pairs of thoracic ap- 

 pendages; first pair of antennae often minute, second pair very large, 



• See "Notes on Cladocera," by E. A. Birge, Trans. Wis. Acad., Vol. 4, 1878. 

 "List of Crustacea Cladocera from Madison, Wis.," by same, ditto, Vol. 8, 1891. 

 "Notes on Cladocera," by same, ditto, Vol. 0, 1892. "Synopsis of the Ento- 

 niostraca of Minnesota," etc., by C. L. Ilorrick and C. II. Turner, Second K p. of 

 State Zool., 1895. "The Cladocera of Nebraska," l)y Charles Fordycc, Stud, from the 

 Zool. Lab. of the Univ. of Neb., No. 42, 1901. 



