18 BULLETIN 140, UNITED STATES NATIONAL MUSEUM 



Subfamily Amidostominae Travassos, 1920b 



Subfamily diagnosis. — Amidostomidae (p. 17) : Characters of the 

 family. 



Type genus. — Amidostomum Railliet and Henry, 1909. 



Although this family and its subfamily are a little difficult to 

 characterize, it appears desirable to have these groups to cover the 

 included genera, Amidostomum and E pomidiostomum. These genera 

 appear to be closely related in their general characteristics and in 

 their locations in bird hosts. The presence of a reduced buccal cap- 

 sule in a bursate nematode which has affinities in other respects with 

 the trichostrongyles suggests that Amidostomum is a transitional 

 form between the trichostrongyles and the group of strongyles with 

 a buccal capsule, a group here regarded as the Strongyloidea. Epo- 

 midiostomum has a buccal capsule, according to Seurat, but accord- 

 ing to Skrjabin, it does not have a buccal capsule; its affinities ap- 

 pear to be with Amidostomum in any case. The combination of a 

 buccal capsule and trichostrongyle affinities has caused a diversity 

 of opinion among helminthologists as to the group to which such 

 worms should be referred, Travassos referring them to the Strong- 

 ylidae and Skrjabin and Seurat to the Trichostrongylidae. While 

 the decision as to the closest affinities of transitional forms does not 

 appear to be very important, some decision must be made and the 

 present writer is inclined to concur with Skrjabin and Seurat in re- 

 ferring them to the trichostrongyles. In passing it may be noted 

 that the cuticular cephalic structures of amidostomes are very simi- 

 lar to those of the spirurids in birds, and that another spirurid, lack- 

 ing a strongyle bursa, as for instance, Rictularia, has a buccal 

 capsule. 



KEY TO GENERA OF AMIDOSTOMINAE 



1. Mouth followed by a globular depressed buccal capsule provided with pointed 

 teeth at its base. Head without 4 outwardly directed papillae and 2 pos- 

 teriorly directed epaulets. Spicules divided into 2 branches. Gorgeret 



or telamon present Amidostomum, p. 19. 



Mouth with a much reduced buccal capsule (Seurat) or without buccal cap- 

 sule (Skrjabin). Head with 4 outwardly directed papillae and 2 pos- 

 teriorly directed epaulets. Spicules divided into 3 branches. Gorgeret or 

 telamon absent Epomidiostomum, p. 26. 



Since the above key was written, Boulenger (1926) has made a 

 new genus, Pseudamidostomum, which probably should be included 

 in this subfamily ; however, since the male is unknown, only a tem- 

 porary assignment can be made. This genus (see Addenda, p. 383) 

 differs from Amidostomum in having no teeth at the base of the 



