C. L. Boulenger 207 
My investigations of the new material have led me to a quite opposite 
conclusion, and I am convinced that Dujardin and von Linstow have dealt 
with the same species. The specimens before me agree in all important charac¬ 
ters with S. polygyrus as described by the French author; at the same time it 
is quite easy to reconcile my account of the male bursa with von Linstow’s 
description and figures. The confusion has been due largely to the latter’s 
mistake with regard to the position of the vulva of the female, but partly 
also to a misunderstanding of Dujardin’s original description by some recent 
authors. 
Dujardin’s specific diagnosis of S. polygyrus clearly shows that one of the 
important characters of the species is the shape of the female tail, the latter 
being narrow, conical, truncated posteriorly and terminated by a slender, 
transparent spike 0*02 mm. in length; the anus is given as 0-075 mm. from the 
posterior extremity. The shape of the tail is therefore very similar to that 
found in species of the genus Nemalodirus. 
Hall (1916) has evidently misunderstood Dujardin’s account, in his 
diagnosis he gives “Tail 20/x long, thin, conical, diaphanous, truncated, and 
terminating abruptly in a narrow point. Anus 75p, from the tip of the tail,” 
further commenting on the fact that Dujardin evidently does not regard 
the length of the tail and the distance from the anus to the tip of the tail as 
the same thing. Dujardin’s actual words are “ queue amincie, conique, tronquee, 
et terminee brusquement par une pointe grele, diaphane, longue de 0 mm., 02;’ 
anus a 0 mm., 075 de Textremite.” The measurement 0-02 mm. here clearly 
refers to the length of the terminal spike, not to that of the tail. 
It is evident therefore that in the shape of the female tail, with its truncate 
extremity and terminal spike, we have an important character which dis¬ 
tinguishes S. polygyrus from S. costellatus, the type species of the genus 
Heligmosomum. The form examined by von Linstow clearly possessed this 
character, the anus being described as 0-098 mm. from the end of the tail and 
definite reference made to a slender, terminal spike, 0-016 mm. long. 
Von Linstow desciibed the vulva as 0-24 mm. from the head end, one of 
the chief characters used by Hall and Travassos in separating S. polygyrus 
v. Linst. from S. poly gyrus Duj.; this statement I think, however, should be 
regarded as a clerical error, Kopfende having been accidentally substituted 
for Schwanzende. The distance 0-24 mm. from the head end would place the 
vulva anterior to the termination of the oesophagus, an almost impossible 
situation in this group of Nematodes; von Linstow’s description of the 
ovejector (1882) is, moreover, incompatible with such a forward position for 
the vulva. 
The specimens obtained by me from the Birmingham voles agree with 
those described by Dujardin and von Linstow in so far as the shape of the 
tail and the position of the anus are concerned. The vulva was found to be 
situated 0-24—0-35 mm. from the posterior extremity. 
Dujardin s account contains little useful information with regard to the 
