322 ILLINOIS BIOLOGICAL MONOGRAPHS [322 



EXPLANATION OF PLATE 



Fig. 14. — Protcocephalus exiguus La Rue, head, toto. 



Fig. 15. — Protcocephalus filicollis (Rud).= ambiguus (Dujardin), head drawn 

 from Schneider's in toto preparation. 



Fig. 16. — Protcocephalus esocis (Schneider), head, drawn from a specimen 

 cleared in glycerine. 



Fig. 17. — Protcocephalus perplexus La Rue, head, toto. 



Fig. 18. — Protcocephalus ambloplitis (Leidy), head, toto. From material col- 

 lected at Walnut Lake, Mich. 



Fig. 19. — Proteocephalus ambloplitis (Leidy), head, toto. From material col- 

 lected at Walnut Lake, Mich. 



Figs. 20, 21 and 22. — Proteocephalus dubius La Rue, heads, toto, showing fifth 

 sucker and contraction states of the suckers. 



Fig. 23. — Proteocephalus fallax La Rue, head, toto, showing fifth sucker. 



Fig. 24. — Proteocephalus singularis La Rue, head, toto. Apical prominence 

 contracted. 



Fig. 25. — Protcocephalus singularis La Rue, head, toto. Apical prominence 

 extended. 



Fig. 26. — Ophiotacnia filaroides La Rue, head of adult, toto. After La Rue 1909. 

 Fig. 27. — Ophiotacnia filaroides La Rue, head of plerocercus, toto, showing 

 vestigial fifth sucker after atrophy is well under way. After La Rue 1909. 



Fig. 28. — Ophiotacnia filaroides La Rue, head of plerocercus, toto, showing 

 outline of hypertrophied fifth sucker. After La Rue 1909. 



Fig. 29. — Proteocephalus pinguis La Rue, head, toto, dorsal or ventral view. 

 Fig. 30. — Proteocephalus pinguis La Rue, head, toto, dorsal or ventral view. 



Fig. 31. — Proteocephalus pinguis La Rue, head, toto, lateral view. Figs. 29, 30, 

 and 31 are from lot 8, Sebago Lake. Ward Collection. 



Fig. 32. — Protcocephalus pinguis La Rue, head and regions of strobila, toto. 

 From material collected at Walnut Lake, Mich. 



Fig. 33. — Crepidobothrium gerrardii (Baird), head, toto. After Smith 1908. 



Fig. 34. — Crepidobothrium gerrardii (Baird), head, toto. After Smith 1908. 



Figs. 35 and 36. — Proteocephalus pinguis La Rue, heads, toto, showing varia- 

 tion in contraction states. From material collected at Walnut Lake, Mich. 



Fig. 37- — Ophiotacnia marenzelleri (Barrois), head, toto, after Schwarz. 



Fig. 38. — Ophiotacnia grandis La Rue, head, toto, showing swollen region back 

 of head. 



