OLIGOCHJSTA 305 



FAMILY 1. ^EOLOSOMATIDAE. 



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- 

 chaets, reproducing by division: 1 genus. 



.ffioLOSOMA Ehrenberg. With the characters 

 of the family: about 9 species, 5 in this 

 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 

 red; length 1 mm., with 7 to 10 segments: 

 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 



algae. 



FAMILY 2. DISCODEILIDAE. 



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 chitinous 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: 



! One pair testes 1. BBANCHIOBDELLA 



a a Two pairs testes. 



Z>! No dorsal appendages 2. BDEIXODRILTJS 



6 2 Dorsal appendages present 3. PTEEODRILUS 



1. BRANCHIOBDELLA* 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 s.eg-r. 

 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. 



*= See "On Some Leechlike Parasites of American Crayfishes," by J. P. Moore, 

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



L sun.,, yoi, ti,; o. 100, 190,6.. 



