44 ILLINOIS BIOLOGICAL MONOGRAPHS [44 



(1900) described an American species of cestode under the name Pro- 

 teocephalus filicollis (Rud.). In a note he changed the name to Proteo- 

 cephalus ocellata (Rud.). He accepted Kraemer's statement that 

 Rudolphi's Taenia ocellata and T. filicollis were identical. For this form 

 which proves to be a new species La Rue (1911) proposed the name, 

 Proteocephalus exiguus La Rue. Schneider (1902:21-23) reported a 

 parasite from Perca fluviatilis, in Finland, as Ichthyotaenia filicollis 

 (Rud.). This form he later (1903:13 and 1905:15-17) considered to be 

 identical with O. F. Miiller's Taenia percae. Schneider (1902:84, 86- 

 87) reported a specimen from Gasterosteus pungitius as Ichthyotaenia 

 filicollis (Rud.). In a later paper (1905:21-24) he considered this form 

 to be Ichthyotaenia ambigua Dujardin and here he gave the first good 

 description of this species. Liihe (1909) gave a diagnosis of this species 

 under the name Ichthyotaenia ambigua Dujardin. His diagnosis added 

 nothing to the data given by Dujardin (1845) and Schneider (1905). 

 La Rue (1911:473, 474, 475) presented some of the conclusions that 

 are given in the present paper at greater length. 



The name Taenia gasterostei as proposed by Gmelin (1790) for this 

 species is not available because it was first used by Muller (1782) to 

 designate the species now known as Schist occphalus solidus. For the 

 same reason the name Alysclminthus gasterostei Zeder (1800) is ren- 

 dered invalid. The name Taenia filicollis Rudolphi (1802) being first 

 used to indicate this species remains available. The generic name is 

 Proteocephalus as indicated by Weinland (1858). It is of importance 

 here to determine the systematic position of the specimens reported by 

 Grimm (1872) and by Schneider (1902 and 1905). A careful compari- 

 son of their descriptions with Dujardin 's (1845) description of Taenia 

 ambigua shows that they evidently belong to the latter species. One 

 notes that Grimm's material was found in Gasterosteus aculeatus while 

 Schneider's specimen came from G. pungitius, and a consideration of 

 these data at once precipitates the question as to the possibility that 

 T. ambigua Dujardin and T. filicollis Rudolphi might not prove to be 

 identical and hence synonymous. The answer to this question must be 

 sought in the study of the collection records and in a comparison of the 

 structures of the forms involved. 



In regard to habitat one may present certain general considera- 

 tions that should have weight. The identity of the two forms can not 

 be considered proven because they have been found together in a single 

 host or separately in different members of a host species, for numerous 

 instances could be cited in which a species or an individual of that 

 species served as host for two or more closely related species of cestode. 

 Nevertheless, it is true that a knowledge of the host is considered to 



