ACANTHOCEPHALA 77 



a rather marked enlargement in the diameter of the body. In some specimens 

 this was especially conspicuous as a hump upon the ventral surface. A crater- 

 like depression observed on this prominence in two individuals superficially 

 resembled a sucker but closer observation demonstrates that such a depression 

 is probably due to a mutilation of the body surface caused by the accidental 

 extraction of one or more of the cuticular spines. 



None of the females collected by the Expedition contained fully formed 

 embryos, consequently data for the comparison of these structures with those 

 of closely related species are entirely wanting. 



Infestation by this parasite does not seem to be excessive for in ten 

 specimens of the host examined but six of the parasites were encountered. 



Habitat: Intestine of Caranx georgiamis C. V. taken at Masatierra by Mr. 

 K. Backstrom in December 1916 and April 1917. 



Cotypes deposited in the Riksmuseum i Stockholm and in the collection 

 of the writer in Urbana, Illinois, U. S. A. 



Until recently all Acanthocephala possessing body spines and occuring 

 as adults in the intestine of fishes have been considered as belonging to the 

 single genus RJiaditiorJiynchus. Such a purely external character has but little 

 value in the determination of phylogenetic relationships. Recently the writer 

 (Van Cleave 1920) has erected a new genus, Quadrigyrtis, for which it has 

 been shown that internal structure and finer morphology rendered it impossible 

 to include this genus even in the same family with Rhadinorhynclms despite 

 the fact that both these genera are characterized by the presence of spines on 

 the body wall. 



There are frequent references in the literature on fish parasites to Acan- 

 thocephala bearing body spines but in most of these instances facts concerning 

 the internal organization of the body are entirely wanting. Many such species 

 were described in the epoch during which the genus EchinorJiynchiis was the 

 only one recognized by most workers for the entire group of the Acanthocephala. 

 As a result, many of the species descriptions of older workers such as DiESING 

 and some of the relatively recent descriptions such as that of EcJi. orestiae by 

 Neveu-Lemaire (1905) are completely lacking in details of morphology that 

 are essential for any determination of their generic relationships. It is entirely 

 possible that some of these insufficiently known species may properly belong 

 in genera previously recognized or may necessitate the erection of new genera 

 after their morphology is more completely understood. At present, on the 

 basis of purely external characters it is safer to allow them to remain unplaced 

 until actual determinations of relationships are possible. 



Specimens from the intestine of Malacopterus reticulatus C. V. taken on 

 Masatierra display unique characters with reference to the structure of the 

 proboscis (Figs. 6 and 7) and the location of the brain. It has been found 

 necessary to erect a new genus to accomodate these peculiar forms. Later 

 study may show that some of the imperfectly known species bearing body 

 spines may come within the scope of this same genus. 



