OLIGOCHjETA 305 



Family 1. iEOLOSOMATIDAE. 



Microscopic fresh-water worms usually with brown, red, or yellow 

 oil globules in integument, giving them a spotted appearance; no dis- 

 sepiments present ; setae in 4 bundles in each segment, of 1 to 6 setae 

 each ; clitellum only on ventral side on segments 

 5 to 7; nervous system hypodermic; prostomium 

 ciliated ventrally; the most primitive oligo- M^, 



chaets, reproducing by division: 1 genus. v^Vj 



JBoLOSOMA Ehrenberg. With the characters J| 



¥W M% 



of the family: about 9 species, 5 in this ^i^^i^, 

 country. 



A. quaternarium Ehr. (Fig. 480) {A. venu- 

 stum Leidy). Head of same width as body; 

 setae sharply bent, those of the same bundle of 

 the same length; the worm encysts itself; spots ^olosoIa%uaUrnaHum 

 red; length 1 mm., with 7 to 10 segments: ^^^'^nStlry^!^''''^^ 



among algae. 



A. hemprichi Ehr. Head broader than body; setae nearly straight; 

 spots red or crimson; length 2 to 5 mm., with 4 to 13 segments: among 



^ ^^^* Family 2. DISCODRILIDAE. 



Small parasitic oligochaets which were formerly grouped with the 

 Hirudinea, with a sucker at the hinder end of the body and without 

 setae, which live on the gills or the outer surface of crayfish ; mouth with 

 a dorsal and a ventral cliitinous jaw; anus dorsal; 2 pairs of nephridia; 



1 or 2 pairs testes; single median genital pore in sixth segment: several 

 genera. 



Key to the genera of Discodrilidae here described : 

 Oi One pair testes 1. Beanchiobdella 



02 Two pairs testes. 



&i No dorsal appendages 2. Bdellodrilus 



62 Dorsal appendages present 3. Pterodrilus 



1. Beanchiobdella* Odier. Dorsal and ventral jaws similar; 1 

 pair testes in fifth segment: 3 American species. 



B. pulcherrima Moore. Body 6 mm. long and 1.3 mm. wide, very 

 transparent forward and somewhat flattened; eighth and ninth seg- 

 ments flattened, each with a pair of adhesive organs : North Carolina. 



B. instabilia Moore. Body 5.5 mm. long, 1.3 mm. wide; hinder 4 

 segments forming a flattened disc-shaped expansion which is almost as 

 wide as long, anterior segment very contractile : eastern states. 



* Soe "On Some Lecchlike Parasites of American Craj'fishes," by J. P. Moore, 

 Proc. Ac. Nat. Sci., Phila., 1893, p. 419. "Notes on Branchiobdella," by W. M. Small- 

 wood, Biol. Bull., Vol. 11, p. 100, 1906. 



