KO. 2346. TWO NEW ACANTHOCEPBALOUS WORMS— VAN CLEAVE 459 



The retracted proboscis and the invertor leave little room for other 

 structures within the interior of the proboscis receptacle. The form 

 and structure of this last-mentioned organ differ considerably from 

 those of other members of this same family. The posterior end of the 

 receptacle is bluntly truncated, and from the dorsal and ventral mar- 

 gins of this posterior surface the retractors of the receptacle emerge 

 (fig. 5). The central nervous system, a single ganglionic mass, lies 

 against the posterior wall of the receptacle between the points of emer- 

 gence of the retractors. The ganglion is about &)[>. in diameter. In 

 other species of Neoechinorhynchidae the wall of the receptacle is 

 composed of a single heavy muscular layer, the fibers of which are 

 directed perpendicularly to the surface of the receptacle. In Pando- 

 sentis iracundus the wall of the receptacle is extremely thin and devoid 

 of any conspicuous development of musculature. The dorsal and ven- 

 tral retractors of the receptacle extend through the body cavity to 

 the dorsal and ventral surfaces of the body wall, respectively, and 

 find their insertion in the immediate vicinity of the giant nuclei of 

 the subcuticula. 



Seven species of fish were found to harbor Acanthocephala in the 

 immediate vicinity where Pandoscntis iracundus was found, yet only 

 two host species are recorded for this parasite. Of these two, Aqui- 

 dem pulcher (Gill) was much the more heavily parasitized. Though 

 all of the collections of this species were made within the limits of 

 one week none of the females taken from Aquidens 'pulcher contained 

 fully formed hard shelled embryos such as were found in some of the 

 individuals from the much less heavily parasitized host, Crenicichla 

 geayL 



QUADRIGYRUS, new genus. 



Generic diagnosis. — Acanthocephala of medium size parasitic in 

 the alimentary canal of fishes. Proboscis armed with four circles of 

 hooks. Anterior surface of body usually provided with four circles 

 of cuticular spines. Subcuticular nuclei of two types; those of an- 

 terior part of body ovoid giant nuclei, dorsal and ventral in loca- 

 tion; those in remainder of body a large, central elongated mass, 

 from which heavy lateral projections are given off, usually lateral 

 in distribution. Proboscis receptacle provided with a single heavy 

 muscular wall. Central nervous system located at posterior ex- 

 tremity of proboscis receptacle. 



Type species. — Quadirgyrus torquatus.^ new species. 



QUADRIGYRUS TORQUATUS, new species. 



Plate 28. 



Specific description. — Preserved individuals long, cylindrical, with 

 a. short globose proboscis; gravid females frequently showing an 

 ovoid enlargement of the anterior extremity. Mature females 10 to 



