336 



CRUSTACEA 



Fig. 521 

 Bosmina longirostris 



(Herrick). 



first antenna ; 2, second 

 antenna ; 3, egg in 

 the brood sac. 



FAMILY 3. BOSMINIDAE. 



First antennae greatly elongated and extending from the beak forms 

 a long curved proboscis; 5 pairs of feet and rudiments of the sixth; 

 second antennae small; pigment spot (accessory eye) wanting; intestine 

 straight and without liver sacs: 1 genus. 



BOSMINA Baird. With the characters mentioned above: about 20 

 species; mostly bottom forms. 



B. longirostris (0. F. Miiller) (Fig. 521). 

 Shell oval with hexagonal markings and with 

 a caudal spine projecting from the ventral 

 margin; length .35 mm.: very common in east- 

 ern and central America; Europe. 



FAMILY 4. LYNCEIDAE. 

 Second antennae small, each branch of 

 each consisting of 3 segments; pigment spot 

 (accessory eye) very large; intestine bent or 

 coiled and usually without liver sacs: the largest cladoceran family, 

 containing about 20 genera. 



Key to the genera of Lynceidae here described : 



! Intestine not coiled or bent 1. EURYCEBCUS 



a, Intestine coiled. 



Z>! A dorsal keel on head 2. ACBOPEBUS 



6 2 No keel. 



c Body oval or elongate. 

 di Outer margin of post-abdomen concave in outline ; second antennae 



with 7 long setae 3. GBAPTOLEBEBIS 



d 2 Outer margin of post-abdomen straight. 



i Terminal claw of abdomen with 1 basal spine. . . . 4. ALONA 



e 2 Two basal spines present 5. PLEUBOXUS 



c 2 Body globular ; animals minute 6. CHYDOBUS 



1. ETTRYCERCUS Baird. Body large and oval with short antennae; 

 intestine bent like an S and with liver sacs : 1 species. 



E. lamellatus (0. F. Miiller) (Fig. 522). Body very large, being 

 sometimes 3 mm. long; hinder side of the abdomen serrate: central 

 states; Europe. 



2. ACROPERTJS Baird. Body minute, elon- 

 gate, with a long, broad abdomen; head and 

 back with a keel; shell with diagonal mark- 

 ings; intestine coiled: 3 species. 



A. harpae Baird (Fig. 523). Body truncate 

 behind ; length .7 mm. : widely distributed over 

 eastern and central America ; Europe ; common. 



3. GRAPTOLEBERIS Sars. Body minute, elongate; posterior margin 

 straight; second antennae with 7 long setae: 1 species. 



Fig. 522 Eurycercus lamel- 

 latus (Siissw. F. Deut.). 



