30 ILLINOIS BIOLOGICAL MONOGRAPHS [,^1 •', 



The material studied by the writer consisted of the following lot of larvae: 

 Nos. 4706 and 4708 of the collection of the United States National Museum; 

 Ch 18a, 16.411, 16.413, 16.414, 16.419, 17.31 and 17.32 of the collection of the 

 University of Illinois, under the care of Professor H. B. Ward; Nos. 49b, 70 

 to 79, 1 10 to 1 19, 361 to 370, 427 and 431c of the collection of Dr. G. R. LaRue ; 

 Nos. II, III, IV, and V from the collection of Mr. H. R. Hill; and Nos. 47, 

 54, 150, 158, 159, 160, 189, 190, 312, 313, 314, 317, 319, and 330 of the writer's 

 collection; and the adults contained in Nos. La 156, 17.184, and 17.185 of the 

 collection of the University of Illinois, respectively from the intestines of 

 Merganser sp., Podilymbus podiceps and Colymbiis holboellii, and No. 387g of the 

 collection of Dr. LaRue from the intestine of Mergus merganser. 



SCHISTOCEPHALUS Creplin 1829 



Bothria and external segmentation developed in the larva. The tip of the 

 scolex retractile. Segmentation complete and corresponding to the internal 

 structure of the animal. Longitudinal and transverse muscles arranged in 

 several alternating layers (three transverse layers enclosing two longitudinal 

 layers). 



Type (and only) species: Schistocepliahis solidus (O. F. Miiller). 



SCHISTOCEPHALUS SOLIDUS (0. F. Miiller 1776) 



