12 ILLINOIS BIOLOGICAL MONOGRAPHS [300 



14 (1, 15) Eggs with thin shells and no opercula. Opening of cirrus and vagina 



marginal, that of uterus at the same level or slightly behind it 

 and ventral. Segmentation very distinct and regular. 



Subfamily MARSIPOMETRINAE Cooper 1917 . . p. 70 

 Type and only genus: Marsipometra Cooper 1917 . . p. 70 

 Type and only species: M. hastata (Linton 1898) . . p. 71 



15 (1, 14) Eggs with thin shells and no opercula. Opening of cirrus and vagina 



dorsal and behind the ventral uterus-opening, or marginal in 

 which case sementation is not well expressed. 



Family PTYCHOBOTHRIIDAE Luhe 1902 . . 16 



16 (27) Opening of cirrus and vagina surficial. 



Subfamily PTYCHOBOTHRIINAE Luhe 1899 . . 17 



17 (26) Scolex elongated, with prominent terminal disc. Segmentation 



well developed, neck absent. 



Bothriocephalus Rudolphi 1808 . . 18 



18 (23) Scolex not pronouncedly constricted posteriorly 19 



19 (20) Uterus-sac occupies one-sixth of the transverse diameter of the 



proglottis B. scorpii (Miiller 1776) . . p. 96 



20 (19) Uterus-sac occupies one-third of the transverse diameter of the 



proglottis 21 



21 (22) Scolex small B, claviceps (Goeze 1782) . . p. 114 



22 (21) Scolex large, terminal disc deeply notched surficially, sagittate in 



lateral view B. cuspidatus (Cooper 1917) . . p. 123 



23 (18) Scolex constricted posteriorly 24 



24 (25) Terminal disc deeply notched laterally as well as surficially; vagina 



pro\ided with a bulbous sphincter near its opening 



. . . . B. manubriformis (Linton 1889) . . p. 133 



25 (24) Terminal disc rectangular; no vaginal sphincter 



B. occidmtalis (Linton 1898) . . p. 149 



26 (17) Scolex almost spherical; walls of each bothrium fused to form a 



hollow organ of attachment with a small anterior opening 



Clestobothrium Liihe 1899 

 Type and only species: C. crassiceps (Rudolphi 1819) . . p. 154 



27 (16) Opening of cirrus and vagina marginal. 



Subfamily AMPHICOTYLINAE Liihe 1902 . . 28 

 Onlygenus represented Abothrium van Beneden 1871. 



28 (29) Pseudoscolex in adult. Longitudinal muscles in bundles. Vitelline 



follicles entirely within the longitudinal muscles. 



A. rugosum (Batsch 1786) . . p. 172 



29 (28) Scolex typical, but variously shaped. Longitudinal muscles not 



in bundles. Vitelline follicles among the longitudinal muscles 

 or outside of them A. crassum {hloch. 1119) . . p. 186 



