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 georgianus 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 Rhadinorhynchus. 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, Quadrigyrus, 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 Rhadinorhynchus 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 Lchinorhynchus 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 D1ESING 
and some of the relatively recent descriptions such as that of Ech. 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 Walacopterus 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. 
