462 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. ..» 



which are only imperfectly known. It is believed that the relation- 

 ships of the forms now considered as belonging to the Echinorhyn- 

 chidae may be better understood and more intelligently dealt with 

 when greater numbers of genera have been discovered through re- 

 searches upon the parasites of regions which have been practically un- 

 studied. 



The presence of four circles of proboscis hooks in Quadrigyurus is 

 a rather significant feature in that it marks a transition between the 

 condition of three circles characteristic of many species of the 

 Neochinorhynchidae and the condition of many circles such as are 

 characteristically found in the genus Rhad'morhynchus and many 

 others. Liihe (1904 : 191 ) has called attention to the fact that in mem- 

 bers of the genus Neoechinorhynchus the hooks usually considered as 

 belonging to the terminal circle do not all occur at the same level upon 

 the surface of the proboscis, but rather represent two alternating 

 series or circles of three hooks each, but slightly separated one from 

 the other. Phylogenetically it seems probable that a condition such 

 as that mentioned by Liihe, and the fusion of two circles at the base of 

 the proboscis (Van Cleave, 1919:238), as in Pomphorhynchus bul- 

 hocolli,, may represent either an early step in the diversification which 

 has resulted in the development of the highly armed, elongated pro- 

 boscis from a simple type, or may, on the other hand, represent a late 

 stage in the regressive simplification of the elongated type of proboscis 

 toward the simple ovoid type. These two possibilities of interpreta- 

 tion are mentioned here because of the fact that investigators have 

 apparently been agreed in defining the simplicity of the Neoechinor- 

 hynchidae as primitive when there is just as much reason for believ- 

 ing that it is a simplicity derived from a regressive evolution. Re- 

 gardless of the interpretation that is put into the evidence it neverthe- 

 less holds that the four circles of hooks on the proboscis of Quad- 

 rigyrus represents a condition intermediate between the fixed three 

 circles characteristic of many Neoechinorhynchidae and the many 

 circles found in most of the other Acanthocephala. In this degree 

 Quadrigyrus represents a transitional form linking the Neoechino- 

 rhynchidae with the other genera. 



To the present time members of the subfamily Rhadinorhynchinae 

 have comprised the only Acanthocephala possessing body spines 

 which occur as adults in fishes. This would suggest a probable rela- 

 tionship between the Rhadinorhynchinae and members of the genus 

 Quadrigyrus. In details of structure the body spines in the two in- 

 stances differ considerably. Those of Quadiigyrus have a less con- 

 spicuous cuticular elevation surrounding each spine, and at the base 

 of each there is a distinctly granular area which renders the boundary 

 between the base of the spine and the subcuticula rather indistinct in 



