86 ILLINOIS BIOLOGICAL MONOGRAPHS [86 



longer in proportion to the proglottid width. The uterine pouches may 

 be more numerous and the embryos a trifle larger than in P. fallax. The 

 second egg membrane is larger in this species. In other respects 

 the species are much alike. Staining and careful comparisons are nec- 

 essary to distinguish them. P. duhius may be differentiated from P. 

 neglectus by the smaller size of its proglottids and by the larger size of 

 its embryos. The proportions of the cirrus-pouch are also very differ- 

 ent. P. duhius is much unlike P. percae and P. cernuae in size, in size 

 of suckers ; in number and size and arrangement of testes, and in length 

 of cirrus-pouch. This species differs from P. esocis, P. agonis and P. 

 filicollis in size and in the presence of a fifth sucker. There is also con- 

 siderable difference in the length of the cirrus-pouch. 



PROTEOCEPHALUS CERNUAE (Gmelin) La Rue 

 [Figs. 5, 6, 66-68] 



Specific Diagnosis: Characters of genus. Strobila short, robust. 

 Observed length as much as 40 mm. Maximum breadth 1.50 mm. Num- 

 ber of proglottids 50-60. Segmentation not plain. Head not well set 

 off from neck, flattened dorsoventrally, and with a flat anterior face. 

 Breadth of head 0.291-0.316 mm., length about 1.10 mm. Suckers not 

 prominent, directed anteriorly, placed above broadest zone of head. 

 Suckers almost globular, heavily muscled, small, with deep cavities. 

 Diameter of suckers 0.064-0.090 mm. Fifth sucker present, 0.024 mm. 

 in diameter. Neck 0.3-0.39 mm. broad, 1.7-2.0 mm. long. First pro- 

 glottids much broader than long, 0.425 mm. broad by 0.085 mm. long. 

 Mature and ripe proglottids broader than long. Length exceeds 

 breadth only in old ripe proglottids. Dimensions of mature proglottids 

 about 0.476 mm. long by 0.816 mm. broad, ripe proglottids 1.309-1.51 

 mm. broad by 0.68-0.85 mm. long. End-proglottid present and func- 

 tional. 



Common genital sinus situated near middle of lateral margin of 

 segment, irregularly alternating. Cirrus-pouch 0.185-0.228 mm. long. 



