108 ILLINOIS BIOLOGICAL MONOGRAPHS [108 



An examination of the preceeding table makes evident that the 

 differences between Schneider's Proteocephalus percae and his P. ocel- 

 latus are so slight that one would not be justified in considering these 

 forms as varieties. Schneider dealt with a single species which ac- 

 cording to the rule of priority should be known as Proteocephalus percae 

 (Muller). 



Proteocephalus percae in some respects resembles P. agonis Bar- 

 bieri, P. exiguus La Rue and P. pusillus Ward. It, however, is so much 

 larger than these species that the possibility of an identity is entirely 

 precluded. P. percae in many ways resembles P. fallax La Rue but it 

 is larger than that species. The character of its proglottids is greatly 

 different. P. percae has many more and larger testes, a longer cirrus- 

 pouch, a much larger ovary, more voluminous vitellaria, a larger head, 

 larger suckers, and larger sucker openings. P. fallax has a larger num- 

 ber of preformed uterine pores. It also has larger embryos. The area 

 occupied by the ovaries of ripe proglottids is triangular in P. fallax but 

 much elongated in P. percae. P. percae resembles P. cernuae in the 

 size of the head, in the size and character of the fi£th sucker, in the shape 

 of the ovary, and somewhat in the character of the proglottids. P. 

 percae, however, has larger suckers with larger sucker openings, a longer 

 and more slender neck, a much longer cirrus-pouch, and fewer and 

 smaller testes. The relationship of cirrus-pouch and vagina are greatly 

 different in the two species. In P. percae the vagina crosses the cirrus- 

 pouch near the middle of the latter while in P. cernuae the vagina does 

 not cross the cirrus-pouch. P. cernuae may have more uterine pouches 

 and its embryos are larger than in P. percae. Further points of dif- 

 ference between P. percae and P. cernuae may be readily noted in an 

 examination of the comparative table of Proteocephalus species (vide 

 infra). 



P. percae in some respects resembles P. longicollis as described by 

 von Linstow but it differs in the number of uterine pouches, number of 

 testes, length of cirrus-pouch, and in the size of eggs and of suckers. 

 P. percae most closely resembles P. pinguis La Rue. The heads of the 

 two species are of about the same size. The suckers are much alike but 

 the fifth sucker is much better developed in P. pinguis than in P. percae. 

 P. pinguis is more slender, its proglottids more nearly quadrate and 

 thicker than in P. percae. P. pinguis has many more uterine pouches 

 and preformed uterine pores. Its cirrus-pouch is less than half as long 

 as that of P. percae. P. percae is readily differentiated from P. torulosus 

 by reason of the total lack of a fifth sucker in the latter. In number of 

 uterine pouches, length of cirrus-pouch and in numerous other ways these 

 species are very dissimilar. 



