C. L. Boulenger 
421 
Railliet and Henry (1902) were the first to show that the three species 
of Sclerostomum, as well as representatives of the three other genera 
established by Looss ( Cylichnostomum, Triodontophorus and Gyalo- 
cephalus), were of common occurrence in European countries and were 
abundantly represented in the Alfort collections. Leiper’s (1910) list 
of species found in horses from the London area shows that the same 
genera occur in this country and we are indebted to the researches of 
Sweet (1909) and Gough (1908) for a few records of equine Sclerostomes 
in Australia and South Africa, respectively. 
Much remains, however, to be done on this subject especially in 
England where the parasites of horses have not attracted the attention 
of helminthologists during recent years. 
My interest in the subject was aroused in the spring of 1915 when 
the attention of the Birmingham Research Department, under Professor 
F. W. Gamble, F.R.S. 1 , was directed to important outbreaks of Sclero- 
stomiasis in horses in certain districts of Worcestershire. Thanks to 
the kindness of Mr J. A. Gold, M.R.C.V.S., of Redditch, I have been 
able to examine a number of infected animals and to assist in post¬ 
mortem investigations of cases which have had a fatal termination; 
specimens were also obtained from “knackers” in different parts of the 
Birmingham area and I am also indebted to Mr Brailsford of the 
Birmingham Health Department for some interesting material. 
Sclerostomes are undoubtedly responsible for a considerable amount 
of damage to horses in this country; before any serious measures can 
be taken for the prevention and eradication of the disease it is absolutely 
essential that a good deal of information be obtained with regard to 
the distribution, frequency of occurrence and life-histories of the 
different forms connected with Sclerostomiasis. Such information is 
gradually being obtained; in view however of the large number of species 
met with during the course of my investigations it has been thought 
advisable to publish a systematic account of the different Sclerostomes 
observed before proceeding to any discussion of their bionomics or 
pathogenicity. 
The present paper deals exclusively with the two genera Trio¬ 
dontophorus Looss and Oesophagodontus Railliet and Henry; of the 
former little seems known in England, whilst the latter has previously 
been observed in India and Burmah only. 
1 I wish to take this opportunity of expressing my thanks to Professor Gamble for 
suggesting this line of research and for his assistance in obtaining material from various 
sources. 
