PHYLLOPODA 



335 



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

 younu" females has from 1 to 4 shar}) teeth: Wisconsin and Minnesota. 



D. pulex DeGeer. The common daphnia (Fii;". 516). Body oval, 

 often reddisli ; 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 Leydig (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 — Scapholeheris mucronata (Herrick). 

 Fig. 519 — Simocephalus vetiilus (Stissw. F. Deut.). 



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

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



3. Simocephalus 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- 

 cies; in muddy swamps, often in ^.^ 520— Ifoma hrachiata (Herrick). 

 impure w^ater. 



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. 



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

 eastern and central America; Europe. 



