36 ASCAROIDEA 



generally absent. Excretory system typically in the form of 

 lateral canals. Testis usually single. 



We have included in this subfamily several partially 

 parasitic genera which have previously been referred to 

 other groups. The structure of the free-living forms of 

 Rhabdias and Strong yloldes indicates their close relationship 

 to Rhabditis. We have therefore suppressed the family 

 Rhabdiasidae (Railliet, 1915) (= Angiostomidae Braun, 1895). 

 There appears to be no reason why the genera Lepidonema, 

 Hystrignathus and Heth should not also be included in the 

 Rliabditinae, and we have adopted this classification, the 

 family Lepidonemidae (Travassos, 1920 (?)), with its sub- 

 families Lepidoneminae and Hystrignathinae, being therefore 

 discarded. 



The family Mermithidae (Braun, 1883) is considered as 

 having relationships on the one hand with the Rhabditidae, 

 and on the other hand with the Anguillulinidae. It is possible 

 that a more comprehensive study of this highly-specialized group 

 would lead to its inclusion in one of these families. We have 

 accordingly compromised by retaining the family Mermithidae. 



The superfamily Rhabdiasoidea (Railliet & Henry, 1916) 

 (= Angiostomoidea Hall, 1916) included, according to Tra- 

 vassos (1920 (?)), the families Rhabdiasidae, Mermiidae [sc. 

 Mermithidae], Lepidonemidae, Isakidae and Atractidae. 

 Isakis, the sole representative of the Isakidae, has been trans- 

 ferred to the Oxyuridae, and the family Atractidae is also 

 regarded as jjart of the order Ascaroidea. This disposes of 

 all the contents of the superfamily Rhabdiasoidea, which 

 accordingly disappears. 



1. Rhabditis Dujardin, 1845. 



Syn. Tribactis Dujardin, 1845; Angiostoma Dujardin, 

 1845, e. p. ; Ascaroides Barthelemy, 1858 ; Pelodytes Schneider, 

 1859 ; Pelodera Schneider, 1866. 



Cuticle smooth or striated. Lateral alae usually absent. 

 Head usually distinct, without lips or with either three or six 

 lips, bearing papillae or bristles. Buccal capsule a cylindrical 

 or three-sided chitinoid tube, usually interrupted by a non- 

 chitinized portion near its posterior end. Oesophagus usually 

 with two swellings, of which the posterior is a muscular bulb. 

 Tail of male with bursa-like alae supported by five to ten 

 pairs of pedunculate papillae. Spicules two, equal, rarely 

 fused. An accessory piece usually present. Testis single, 

 reflexed. Tail of female more or less pointed. Vulva com- 

 monly in the middle of the body, with opposed genital tubes 

 and reflexed ovaries ; more rarely posterior, with a single 

 anterior genital tube. Oviparous, sometimes viviparous. 



