PETLLOPODA 



335 



ing spur present on the dorsal margin of the head, which in males and 

 young females has from 1 to 4 sharp teeth: Wisconsin and Minnesota. 



D. pulex DeGeer. The common daphnia (Fig. 516). Body oval, 

 often reddish ; a prominent beak on the under side of the head ; length 2 

 mm. or more : very common and widely distributed in America and Europe. 



D. hyalina Ley dig (Fig. 517). Body oval; caudal spine almost 

 as long as body; head extended forward in a helmet-like crest but very 

 variable in shape and size; length 1.8 mm.: widely distributed in this 

 country and Europe. 



2. SCAPHOLEBERIS Schodler. Body short with a truncated hinder 

 end from the lower margin of which a pair of caudal spines, which are 

 sometimes very short, extend backwards: 6 species. 



Fig. 517 '' Fig. 518 Fig. 519 



Fig. 517 Daphnia hyalina (Herrick). Fig. 518 Scapholeberis mucronata (Herrick). 

 Fig. 519 Simocephalus vetulus (Siissw. F. Deut.). 



S. mucronata (0. F. Miiller) (Fig. 518). Spines short; color dark; 

 length .8 mm. : common in eastern America and in Europe. 



3. SIMOCEFHALTJS Schodler. Body obliquely truncate behind, with- 

 out a caudal spine; abdomen with 2 dorsal processes: 8 species. 



S. vetulus (0. F. Miiller) (Fig. 519) . Body large, short, and high ; head 

 rounded in front, 2.5 mm. long: common in eastern America; Europe. 



S. serrulatus (Koch). Head narrow, extending forwards sharply; 

 length 2 mm.: central United 

 States; Europe. 



4. MOINA Baird. Head with- 

 out beak; first antennae long; the 

 end of the abdomen not covered 

 by the shell; pigment spot (acces- 

 sory eye) absent: about 10 spe- 



Fig. 520 Moina brachiata, (Herrick). 



cies; in muddy swamps, often in 

 impure water. 



M. brachiata (Jurine) (Fig. 520). Body almost as high as long, 

 greenish in color; 1.3 mm. long: eastern America; Europe. 



5. CERIODAPHNIA Dana. No beak present; first antennae short; 

 head rounded; shell oval or circular, and reticulate: about 20 species; 

 often in foul water. 



0. reticulata (Jurine). Claws of abdomen dentate; length .8 mm.: 

 eastern and central America; Europe. 



