30 BULLETIN 140, UNITED STATES NATIONAL MUSEUM 



Family STRONGYLIDAE Baird, 1853 



Family diagnosis. — Strongyloidea (p. 29) : Vulvo in posterior half 

 of the bodj 7 . Corona radiata usually present. Spicules well devel- 

 oped. Bursa well developed. Parasites of the digestive tract as 

 mature adults. 



Type genus. — Strongylus Mueller, 1780. 



Subfamily Strongylinae Railliet, 1893 



Subfacility diagnosis. — Strongylidae (p. 30) : Forms usually with 

 a corona radiata. Head not bent dorsally. Intestine straight, not 

 greatly convoluted. Bursa with rays long, not reduced. 



Type genus. — Strongylus Mueller, 1780. 



Tribe DELETROCEPHALEAE Railliet and Henry, 1911, emend. Stiles 



and Hassall, 1920 



Synonym. — Deletrocephalae Railliet and Henry, 1911. 



Tribe diagnosis. — Strongylinae (p. 30) : Ventro-ventral and latero- 

 ventral rays close together and parallel, originating from a common 

 stem. Lateral rays originate in a common stem and are typically 

 divergent. Externo-dorsal ray originates at the base of the dorsal 

 ray. Main dorsal ray bifurcates and each branch subdivides in such 

 a way as to have 3 major and minor terminations ultimately. The 

 vulva is close to the anus and the ovejectors and uteri are con- 

 vergent. 



Type genus. — Deletrocephalm Diesing, 1851. 



This tribe is almost too close to the Cylicostomeae to make its 

 tribal characters impressive. The externo-dorsal ray originates at 

 the very base of the dorsal ray, instead of with the lateral rays, 

 but the two conditions approach each other so closely as to leave 

 some doubt as to whether the distinction is of value. Other features 

 are so similar as to make it appear that the point of origin of the 

 externo-dorsal ray in the forms involved can hardly be regarded as 

 of more than generic value. 



KEY TO GENERA OF DELETHOCEPHALEAE 



1. Oorona radiata present. Buccal capsule without teeth or longitudinal sus- 

 taining ribs or rays Codiostomum, p. 30. 



Corona radiata absent. Buccal capsule with longitudinal sustaining ribs or 

 rays and usually with teeth Deletrocephalus, p. 32. 



Genus CODIOSTOMUM Railliet and Henry, 1911 



Generic diagnosis. — Deletrocephaleae (p. 30) : Strongyles with in- 

 ner and outer leaf crown and well developed dorsal gutter. Bursa 



