86 



ILLINOIS BIOLOGICAL MONOGRAPHS 



[374 



It will be noticed that in spite of the fact that all of the measurements of 

 the tridents are larger than those given by Fuhrmann, they are considerably 

 smaller than those of the other type. 



Finally, altho no specimens of either type of larva so young that the hooks 

 had not yet developed were met with, those from the intestine of Stizostedion 

 vitreum were provided with only very small tridents of the nodulosus form, 

 the bases of which were not yet well developed. The whole scolices were a 

 sort of compromise between the two types in shape but of the nodulosus tx'pe 

 as regards size, as shown in the following measurements: Length, 12mm.; 

 width at middle, 0.64; length of scolex, 0.87; width of terminal disc, 0.64; same 

 of scolex posteriorly, 0.80; width of trident, 0.14, length medially, 0.07, ex- 

 ternally, 0.05. Altho these specimens would seem to represent an intermediate 

 stage between the two types of scolex so far as the general shape is concerned, 

 the writer was inchned to consider them as belonging to the nodulosus type; 

 yet it must be said that smaller scolices, e.g., those from M. dolomieu in the 

 table, have considerably larger hooks. 



On the whole, then, the bulk of the evidence given here tends to show that 

 here in America there are probably two species, very closely related to, if not 

 identical with, the European T. nodulosus and T, robustus which have been 

 clearly distinguished by Fuhrmann (1910) and also recognized by Liihe (1910: 

 23). However, no adults have as yet been reported for this continent, so far 

 as the writer is aware. 



The material studied is here listed as a host record also: 



