240 
American hosts, but even more strikingly in the greater diversification of 
structure among the American species. 
Hamann’s description of the Neoechinorhynchidae (1892), based 
upon a knowledge of but one genus comprising two species of monotonous 
similarity, quite naturally emphasized for the family those characters 
which had been selected to characterize his Neorhynchus. The discovery 
of more strikingly diversified American species led the present writer 
(1913) to emend the generic diagnosis in order that N. gracilisentis and 
N. longirostris might be included within the genus Neoechinorhynchus 
(= Neorhynchus). However, more recent study has shown that the 
differences between these two species and the other members of the genus 
are too great to be regarded as of merely specific value. In the descrip- 
tion of N.longirostris (Van C.) the writer (1913 : 182) pointed out the © 
possibility of establishing a new genus for this species, but because of a 
few fundamental points of similarity in body-structure between this and 
other members of the family it was placed in the genus Neoechino- 
rhynchus. Recent further study of Neoechinorhynchidae, made possible 
by the addition of newly discovered species, and a re-study of cotypes of 
N.longirostris have convinced the writer that the arguments originally 
advanced for retaining this species within the genus apply more strictly 
as reasons for its retention within the family. The validity of this posi- 
tion was seen by Professor Henry B. Ward who (1918:547) erected for 
it a new genus, Tanaorhamphus, with N.longirostris (Van C.) as type. 
Inasmuch as the species N. gracilisentis (Van C.) possesses charac- 
ters which give strong evidence of its generic isolation it becomes advis- 
able to create for it a new genus, for which the writer proposes the name 
Gracilisentis, Neoechinorhynchus gracilisentis becoming the type of the 
genus. 
With the accumulation of new information and new interpretations 
of facts regarding members of this family more definite consideration 
should be given to the characterization of the family and of its con- 
stituent genera. In the following synopsis the writer has endeavored to 
describe the family and its genera in a more complete manner than has 
been attempted heretofore. 
Famity CHARACTERS 
Acanthocephala of small to medium size, parasitic as adults in the 
alimentary canal of fishes and reptiles. Wall of proboscis-receptacle a 
single layer of muscle. Brain near base of proboscis-receptacle. Body 
devoid of spines; spines or hooks on proboscis only. Nuclei of subcuticula 
and of lemnisci extremely large, normally of fixed number and definite 
arrangement ; the subcuticula with five in mid-dorsal line of body and one 
in mid-ventral line near anteriar end; the lemnisci normally with two in 
one lemniscus and a single nucleus in the other. Embryos borne inside 
body of females provided with three membranes. Membranes in all 
known species fully concentric, without polar modifications or constric- 
