C. L. Boulenger 
319 
Genus Poteriostomum Quiel, 1920. 
(Hexodontostomum Ihle, 1920.) 
8. Poteriostomum imparidentatum Quiel, 1920. 
(Hexodontostomum markusi Ihle, 1920; Cylichnostomum zebrae Turner, 1920.) 
A single male specimen of this worm was found in company with numerous 
examples of Cylicostomum insigne in the colon of a horse from Sargodha, Pun¬ 
jab. The species was already known from this host in Europe and in W. Africa 
(Yorke and Macfie, 1920 a), it has also been recorded from a Chapman’s zebra 
in the London Zoological Gardens (Turner, 1920). 
The systematic position of the genus has recently been discussed by several 
authors, I agree with Ihle (1920 6) and Yorke and Macfie (1920 a) that it 
should be separated from Cylicostomum. 
Poteriostomum imparidentatum has been fully described on a number of 
occasions, there are however a few discrepancies between the accounts given 
by different authors which, although possibly due to errors of observation, 
may indicate that more than one species have been confused under this name. 
To avoid further confusion I have given figures and a short description of the 
form before me. 
The specimen from the Punjab was a male, 11 mm. in length, with a maxi¬ 
mum thickness of about 0-6 mm. When fresh the body of the worm was of a 
bright, blood-red colour. 
The mouth-collar is well marked off from the rest of the head and is com¬ 
paratively low (Text-fig. 2). The mouth is oval in shape, the dorso-ventral 
axis being somewhat the greater. The sub-median head-papillae are short, 
with broad bases resting on the oral collar; the lateral papillae do not project. 
The elements of the external leaf-crown are small and pointed, numbering 
about 72. The internal crown consists of 38 leaves, larger than those of the 
external leaf-crown, of these six (two lateral and four approximately sub¬ 
median in position) are considerably longer than the others, reaching almost to 
the mouth-opening and moreover projecting further inwards than the smaller 
elements, the latter number six or seven between each pair of long leaves. 
In their key to the species of Poteriostomum, Yorke and Macfie (1920 a) 
give the number of small elements between the longer ones as seven in P. 
imparidentatum, in their figure however they show only six. Ihle (1920 b) 
gives the number as six, seven or eight, whilst Turner (1920) shows as many as 
ten in one part of the leaf-crown (p. 447, fig. 2), three only in another (p. 446, 
fig. 1). The number of leaves in the crown is thus obviously capable of much 
variation and I agree therefore with Ihle (1920 b) in considering P. pluri- 
dentatum Quiel as merely a variety of the type-species. 
The mouth-capsule has a height of about 0-07 mm., the greatest breadth 
in the dorso-ventral axis measuring 0-2 mm. The walls of the capsule diverge 
from before backwards and are considerably thickened posteriorly. 
