NO. 2131. NEMATODE PARASITES OF RODENTS— HALL. 149 



ANALYTICAL KEY TO GENKRA OF HELIGMOSOMINAE. 



1. Two separate dorsal rays, vulva anterior Heligmosomoides, p. 160. 



One branohins dorsal ray, vulva posterior 2. 



2. Body not spirally enrolled, prominent longitudinal cutieular markings. 



HeUgmosomnm. p. 149. 

 Body spirally enrolled, without prominent longitudinal cutieular markings. 



Viannaia. p. 1.58. 



Genus HELIGMOSOMUM Railliet and Henry, 1909a. 



/Synonym. — Strongfylus Mueller, 1780, of authors. 



Generic diagnosis. — Heligmosominae (p. 148) : Usually minute 

 forms. Cuticle of normal tliickness. Body commonly with cutieular 

 markings other than simple striations, the longitudinal markings 

 being especially prominent. Vulva in posterior portion of body, 

 close to anus. -A single ovary present. Uterus provided with well- 

 developed ovijector. Two filiform spicules, less than 1 mm. long; 

 gubernaculum present or absent. Nature of bursal rays not known 

 to me from type-species, but from new species included in this genus 

 is apparently as follows: Ventro- ventral and latero-ventral rays di- 

 vergent, the latero-dorsal ray straight, the ventro-yentral curving 

 posteriorly. The externo-lateral and medio-lateral rays run close 

 together and parallel throughout most of their extent, but their tips 

 diverge distally. The postero-lateral ray diverges from the medio- 

 lateral, curving posteriorly, so that its tip is not far from the tip 

 of the externo-dorsal ray. The externo-dorsal ray is very thin, the 

 thickest rays being the medio-lateral and externo-lateral. The dorsal 

 ra}^ originates as a thick stem, which bifurcates to form tvro long 

 branches, which are cleft near their ends to form two small branches. 

 Between the main bifurcation and the origin of the ray the main stem 

 sends out two small posteriorly directed spurs. The bursa forms, 

 usually, a small dorsal lobe and two large lateral lobes. 



Type-species. — Heligmosomum costell&timi (Dujardin, 184.5) Eail- 

 liet and Henry, 1909«. 



This genus was proposed by Eailliet and Henry by the designation 

 of Strongylus costellatus Dujardin, 1845, as type-species. No generic 

 diagnosis was given and as the species is nowhere adequately de- 

 scribed and nowhere figured, the present writer was unable to de- 

 termine the basis on which the genus was proposed or the probable 

 generic characteristics. The included species are also so poorly 

 described and the existing figures so contradictory that little light 

 was obtained by an examination of these. A request for material 

 of the type or included species was made to Professor Eailliet by 

 Dr. B. H. Eansom, noting the fact that the generic characteristics 

 were not evident from the published descriptions of these species. In 



