506 Mr. H. A. Baylis on 
for diagnosis, are unknown. The species differs from Ch. 
borealis (v. Linst.) in having forty-five to forty-eight testes, 
instead of twenty-five, in each segment, and also in having 
a smaller scolex (0°43 mm. across at the suckers, instead of 
0°67 mm.),. 
Anomotenia campylacantha (Krabbe), Zschokke, 1903. 
Host: Uria grylle. Yukanski, June and July 1917. 
Numerous examples of a worm which may be referred to 
this species occurred in several black guillemots, associated 
in one case with Tetrabothrius intrepidus. They usually 
occupied the upper part of the intestine, just below the 
gizzard. 
Anomotenia micracantha (Krabbe), Zschokke, 1903. 
Host: Uria grylle. Yukanski, 22. x. 1917. 
A second and rather larger species, which I refer to 
A. micracantha, occurred in considerable numbers in one of 
the same birds in a similar position to the preceding form. 
Monopylidium arcticum, sp.n. (Figs. 3 & 4.) 
Host: Tringa maritima (purple sandpiper). Yukanski, 
fo Wilt. 1917: 
This is a slender little worm, about 3°5 cm. long when‘ 
fairly extended. The maximum width (at the posterior end 
of the strobila) is about 0°5 mm. A peculiar feature is the 
tendency of the neck to be very much contacted in the 
longitudinal direction (fig. 3, B) and very wide just behind 
the scolex. Nearly all the specimens show this contraction, 
which gives them, to the naked eye, the appearance of having 
a very large, flattened scolex. 
The scolex (fig. 3, A) measures about 0°24 mm. across the 
suckers, the diameter of the latter being 0°12 mm. The 
rostellum has a mushroom-shaped end and a fleshy and 
muscular stalk. There is a single row of about thirty (?) 
hooks, measuring about 15 w in length. There is a pair of 
glandular (?) structures (fig. 3, A, G.) at the base of the 
rostellum, in the substance of the scolex. 
The strobila contains some eighty segments, which are 
considerably longer than broad, except those near the anterior 
end. ‘They gradually increase in length towards the posterior 
end, some of the gravid segments bemg fully three times as 
long as broad. ‘The longitudinal musculature is very well 
developed. Mature segments (fig. 4) begin to appear at 
