C. L. Boulenger 
317 
the genus belong to three quite distinct species, since discovered by Ransom 
and Hadwen (1918) to be common forms in Canada also. T. senatus and T. 
minor were not recorded from the N. American material, nor were they found 
by me among thousands of specimens examined from horses in England. Our 
present knowledge of the subject therefore seems to suggest that they are 
restricted to tropical and subtropical countries. 
T. senatus is now known from Egypt (Looss, 1902), Ceylon (? v. Linstow, 
1904) and East Africa (Boulenger, 1920). I have also seen undoubted examples 
of this species obtained from horses in Mesopotamia 1 . 
T. minor has been recorded from Egypt (Looss, 1902) and West Africa 
(Yorke and Macfie, 1902 b). I am also able to show in this paper that it is the 
commonest representative of the genus in the Punjab. 
5. Triodontophorus minor (Looss, 1900). 
As mentioned above this species proved to be the commonest form of 
Triodontophorus in the Punjab, it was found, usually in small numbers, in the 
majority of horses examined by me in Lahore. As pointed out by Looss the 
species is remarkable for its habitat in the posterior region of the colon, in the 
Punjab occurring in this situation usually in company with specimens of 
Cylicostomum insigne. 
The Indian specimens of T. minor agree on the whole fairly well with those 
described by Looss from Egypt, there are however a few points to which I 
desire to call special attention and I therefore add a short description of the 
worms observed by me. 
T. minor is a rather small species of the genus Triodontophorus, the Punjab 
specimens measuring: males, 9-12 mm.; females, 11-14 mm. in length. 
The mouth-collar is depressed at the margins (Text-fig. 1, m.c.), the latter 
in some individuals having a tendency to curl forwards. The elements of the 
leaf-crowns number about 50. 
The oral capsule is comparatively large, the breadth being a little greater 
than the height, as shown by the following measurements: height, 0-13-0-17 
mm.; breadth, 0-15-0-185 mm. 
The structure of the capsule-teeth varies considerably in different speci¬ 
mens, in some, as in those described by Looss from Egypt, the anterior mar¬ 
gins are quite smooth, without denticulations, in others, however, such denticu- 
lations occur, a few individuals having the margins of the teeth deeply serrated 
(Text-fig. 1, t). I have shown below that similar variations are found in other 
species of Triodontophorus , the nature of the tooth-margin is therefore not to 
be depended on as a specific character within the genus. 
# 
1 The worms recorded by Leiper (1910) under this name from horses in London were identified 
at a time when only two species of the genus were known. It would seem desirable to re-examine 
this material in view of our present knowledge of the subject before accepting them as belonging 
to Looss’ species. 
