no. 2346. TWO NEW ACANTHOCEPnALOUS WORMS— VAN CLEAVE 461 



The degree of infestations of individual hosts varied widely. Even 

 in Eoplias malabaricus, the type host of this species, infestations 

 ranged from a single parasite to more than 50 individuals in the 

 same host specimen. No extremely heavy infestations were en- 

 countered. 



The position of the genus Quadrigynis in the classification of the 

 Acanthocephala is not easily determined. This is true in spite of 

 the fact that characteristics commonly considered as of value in es- 

 tablishing generic relationships are clearly observable in members 

 of this genus. The difficulty arises from the fact that these char- 

 acters appear in combinations which have not been observed pre- 

 viously in other genera. In the genera and families of Acantho- 

 cephala created by Hamann (1892), and in the later work by Liihe 

 (1911), certain groups of characters seemed so commonly associ- 

 ated that groups rather than individual characters have come to be 

 considered by taxonomists as immutable units forming the basis 

 of a natural classification. The early families were based on a sin- 

 gle genus each and the genera were frequently monotypical, con- 

 sequently it is not surprising that the addition of new facts regard- 

 ing Acanthocephala from other parts of the world should bring 

 together new groupings of characters different from those of the 

 genera and families included in the narrowly restricted regions con- 

 sidered by the early workers. 



Thus, the presence of a single muscular wall surrounding the re- 

 ceptacle of the proboscis was considered as peculiar to the Neoechi- 

 norhynchidae until the present writer (1916«) described several 

 species of Centrorhynchidae belonging to the genus Mediorhynchus, 

 each of which displayed a single-walled receptacle. Now, with the 

 discovery of the genus Quadrigyrus^ another addition is made to the 

 forms having a single-walled proboscis receptacle, and this character 

 may no longer be in itself considered as diagnostic for the Neoechi- 

 norhynchidae. 



In the following discussion of relationships the writer has followed 

 the current usage of including the subfamily Rhadinorhynchinae 

 within the family Echinorhynchidae. As it stands, this family has 

 little homogeneity, representing a residual group from which the other 

 families have been detached in much the same manner as its type 

 genus, Echinorhynchus^ represented at one time the only genus recog- 

 nized among the Acanthocephala. Many of the species attributed to 

 Echinorhynchus have remained there because of insufficient data to 

 enable later workers to recognize the genus to which the species prop- 

 erly belong. A number of slightly related genera still remaining in 

 this family present charactertistic differences of what seem to be of 

 family significance. Conservatism has prevented workers in this 

 group from creating new families for these single genera, many of 



