34 ILLINOIS BIOLOGICAL MONOGRAPHS [34 



KEY TO THE BETTER KNOWN GENERA AND SPECIES OF 

 PROTEOCEPHALIDAE 



1(70) Proteocephalids with heads which have no folds or lappets 



of tissue about the suckers 2 



2(47) Testes lie in a single broad field between vitellaria; para- 

 sitic in freshwater fish. 



Genus Proteocephalus Weinland 1858 3 



3(24) Functional fifth sucker lacking, i. e. absent or vestigial 4 



4(15) Testes number 100 or more _ „ 5 



5( 8) Cirrus-pouch extends j^-J^ across breadth of proglottid „ 6 



6( 7) Uterine pouches 4 to 8 on either side; ductus ejaculatorius 



nearly straight Proteocephalus agonis (Barbieri 1909) 



7( 6) Many uterine pouches on either side; ductus ejaculatorius 

 forming several coils. 



Proteocephalus fossatus (Riggenbach 1896) 

 8( 5) Cirrus-pouch extends less than ys across the breadth of the 



proglottid __ „ 9 



9(12) Genital pore situated at middle of lateral margin of proglot- 

 tid „.. „ „.._ 10 



10(11) Uterine pouches 3 to 4 on either side; testes in 2 layers; cir- 

 rus-pouch extending %-% across the breadth of the 

 proglottid ; suckers 0.18-0.2 mm. in diameter. 



Proteocephalus torulosus (Batsch 1786) 

 11(10) Uterine pouches 7.to 14 on either side; testes in 1 layer, cir- 

 rus-pouch extending Ye-yi across the breadth of the 

 proglottid; suckers 0.095-0.16 mm. in diameter. 



Proteocephalus macrocephalus (Creplin 1825) 

 12 ( 9) Genital pore anterior to middle of lateral margin of pro- 

 glottid 13 



13(14) Uterine pouches 20 to 25 on either side; vagina anterior to 

 cirrus-pouch; 135-155 testes. 



Proteocephalus perplexus La Rue 1911 

 14(13) Uterine pouches 10 to 12 on either side; vagina posterior to 

 cirrus-pouch; about 200 testes. 



Proteocephalus sulcatus (Klaptocz 1906) 



15 ( 4) Testes number less than 100 _ 16 



16(17) Suckers with pointed apex and shallow cavity. 



Proteocephalus singularis La Rue 1911 

 17(16) Suckers round or oval with smooth contour 18 



