During the past few years the writer has had an opportunity of making observations on the quiescent larvæ of Tylenchus tritici occurring in galls from ears of wheat, and of examining certain resting stages of Tylenchus dipsaci from diseased Narcissus bulbs.

1. From an examination of over 700 sheep of Scottish origin a list of the parasites found in the intestinal tract has been prepared.

2. The commonest parasite found is Monodontus trigonocephalus, a worm which occurs also in goats and cattle. This parasite can be found at any season.

3. Nematodirus sp. also is extremely common during the warmer months.

4. From a systematic geographical examination of sheep it has been ascertained that Monodontus trigonocephalus occurs in every district in Scotland ; and of 40 sheep examined in this part of the enquiry, 38 were found to be infected. Thirty specimens have been recovered from an apparently healthy sheep, but usually the number is much smaller (7–10).

Host: Cebus fatuellus. Habitat: Stomach. Locality : South America. Two males and two females were collected from the stomach of a Brown Capucin. The two males are respectively 37 and 41 mm. long by 1.5 and 1.65 mm. thick; the two females are respectively 54 and 60 mm.long by 2.9 and 2.75 mm. thick in their posterior third.

The nematode described in this paper was obtained from the minnow, Leuciscus phoxinus Linn. About 50 minnows were caught in Loch Lubnaig in Perthshire, Scotland. Only two specimens were infected, one with a single female, the other with two females and a male. The worms were found in the mucus of the posterior part of the intestine.

Six species of Trichostrongylidæ are described in this paper. Four are previously recorded species which were insufficiently known and described.