48 ILLINOIS BIOLOGICAL MONOGRAPHS [48 



P. filicollis somewhat resembles P. agonis Barbieri but it may be 

 differentiated from that species by its relatively shorter cirrus-pouch, 

 by a different position of the mass of coils of vas deferens, by its larger 

 testes which are arranged in two layers while the testes of P. agonis 

 are in one layer. P, agonis has no genital papilla while in P. filicollis 

 there is a simulation of one. P. filicollis is readily distinguished from 

 P. duhius La Rue and P. fallax La Rue by its smaller size, by its lack of 

 a fifth sucker, by its more numerous testes, shorter cirrus-pouch and 

 smaller proglottids. The embryos of P. filicollis are smaller than those 

 of P. fallax. P. filicollis differs from P. pusUlus Ward and P. exiguus 

 La Rue in not having a fifth sucker, in having smaller suckers, a smaller 

 head, more testes, and fewer uterine pouches. P. filicollis differs greatly 

 from P. percae in the lack of a fifth sucker, in the size of body, head 

 and suckers, in the proportions of the proglottids, in the size of the 

 cirrus-pouch, ovaries, etc. It likewise differs from P. cernuae in prac- 

 tically the same points as stated for P. percae. P. filicollis is smaller 

 than P. esocis. It has a shorter cirrus-pouch and a larger number of 

 testes. The proportions of the proglottids are different. The two spe- 

 cies are alike in not possessing a fifth sucker. 



PROTEOCEPHALUS ESOCIS (Gui. Schneider) 

 [Figs. 16, 61-63] 

 1905: Ichthyotaenia esocit Gui. Schneider, 1905:19-20 

 1911: Proteocephalus esocis La Rue, 1911:475 



Specific Diagnosis: The characters of the genus. Cestodes small 

 and slender, 1-4.7 cm, long, maximum breadth 0.7 mm. Scolex 0.140 

 mm. broad, 0.105 mm. thick. No fifth sucker, nor vestige of it. Suckers 

 shallow, weak, small, about 0.050 mm. in diameter, directed anteriad. 

 Diameter of sucker opening 0.026-0.032 mm. Neck 2-5 mm. long. Sixty- 

 six proglottids in specimen 4.7 cm. long, youngest proglottids twice as 

 broad as long, 0.370 mm. broad by 0.170 mm. long. Middle proglottids 

 broader than long, 0.680 mm. broad by 0.390 mm. long. Last proglottid 

 longest, 0.650 mm. long by 0.460 mm. broad at anterior end. Segmen- 

 tation not evident. Transverse intersegmental furrows shallow. Sur- 

 face smooth. 



Genital organs as in genus. Genital pore not on genital papilla. 

 Pore marginal, irregularly alternating, about middle of proglottid. 

 Cirrus sheath relatively long, extending nearly to middle of proglottid. 

 Length of cirrus-pouch 0.230-0.250 mm. Cirrus sinuous. Vas deferens, 

 a mass of coils in middle of proglottid. Testes, 30-38 visible in mature 



