434 Sclerostomes of the Horse 
divergence of opinion as to the exact position of the worm in modern 
classifications. 
Looss (1900) was inclined to include S. robustum in his genus 
Triodontophorus ; Railliet and Henry (1902), however, expressed the 
opinion that if Giles’ description and figures were accurate the parasite 
could not be included in any of the known genera, and proposed for it 
the new generic name Oesopliagodontus. In a later paper (1912) these 
authors assign their genus to the sub-family Cylicostomeae, close 
to Cylichnostomum. 
Material was obtained by me near Redditch in Worcestershire on 
one occasion only, from the colon of a mare which had died suddenly 
after showing symptoms of severe sclerostomiasis. About a dozen 
specimens were collected from among an enormous number of Trio¬ 
dontophorus tenuicollis and Cylichnostomum spp., examination of 
these showed that Giles’ description of the species was on the whole 
correct; I have, however, been able to add to his account and my 
observations also show that Railliet and Henry were undoubtedly 
right in their estimate of the systematic position of this interesting 
worm. 
Specific diagnosis. The body is stout, tapering only slightly 
towards the anterior extremity. During life the worms have a brownish 
colour and the intestine is deeply pigmented, showing through the 
semi-transparent body-wall. 
The cuticle is provided with transverse ridges as in Triodontophorus. 
The head is separated from the body by a slightly constricted neck and 
is of considerable breadth, measuring 500-800 g. The mouth-collar is 
depressed and its oral margin considerably notched so as to present a 
tuberculated appearance (Plate XXII, fig. 3). As in the genus Cylich¬ 
nostomum there are anterior and posterior leaf-crowns, each composed 
of distinct leaf-shaped elements; the leaves of the anterior crown are 
large and usually number about 18, those of the posterior crown are 
considerably smaller, they are rather difficult to count, but, as far as 
I could ascertain, their usual number is about 36. 
As in other Sclerostominae six head papillae are present, two lateral 
and four sub-median. The lateral papillae are not markedly raised 
from the surface of the mouth-collar, their bases are rather broad and 
carry a pair of lateral horn-like processes; a pair of similar but smaller 
processes are situated near the anterior extremity of each papilla 
(cf. Plate XXII, fig. 3, L.P.). Each sub-median papilla consists of a 
slender tactile appendage carried on a basal, wart-like prominence 
