C. L. Boulenger 
243 
6. Ostertagia trifurcata Ransom. 
Whilst recently examining a number of specimens of Ostertagia 
circumcincta collected at Wye from the fourth stomach of a lamb 
suffering from parasitic gastritis, I found two male individuals which, 
although obviously belonging to the genus Ostertagia, differed markedly 
from the males of the common species. A detailed study of the 
bursae and spicules showed that these worms were to be referred to 
the rare species Ostertagia trifurcata described by Ransom in 1907. 
This species has been met with in the United States only, in small 
numbers in the fourth stomach and intestine of sheep and goats, and 
always associated with Ostertagia circumcincta ; the occurrence of 0. 
trifurcata in sheep in England is therefore a new fact in its dis¬ 
tribution. 
The female of 0. trifurcata was not found by Ransom ; in the 
material collected at Wye there were, however, two Ostertagia females 
which differ in many respects from the females of 0. circumcincta 
and which I take to belong to the former species. The measurements 
of the male specimens differ slightly from those given by Ransom (1911), 
I have therefore given a fairly complete description of these, as well as 
of the female individuals. 
Males. As mentioned above only two males were obtained from 
the material collected at Wye, these measured 6 and 6-8 mm. in length, 
with maximum breadths of 85 and 98 p,, respectively, in the region of 
the body just in front of the bursa. 
The longitudinal lines of the cuticle are well marked in both 
specimens. 
The diameter of the head is 16 p in the larger individual, 20 p in 
the smaller, the latter has the cuticle slightly dilated in the cephalic 
region. The breadth of the body at the posterior extremity of the 
oesophagus is 60 p. 
The oesophagus has a length of 480-490 p with a maximum thick¬ 
ness of 30-48 p posteriorly. 
The nerve ring and the cervical papillae were observed in the 
smaller specimen only, their distances from the anterior end of the 
body being 210 p and 260 p, respectively. 
The genital bixrsae are somewhat folded in both individuals, when 
spread out they must have had a breadth of between 280 and 300 p. 
The prebursal papillae are conspicuous. 
The arrangement of the bursal rays is similar to that described 
I 
