STUDIES ON THE DIGENETIC TREMATODES. 399 
Blanchard completed the topography of the female genitaha, 
and Looss was the first to indicate the structure of the 
circum-oral papille. Several other important features remain 
undetermined. ‘The systematic position of the species will be 
discussed after a general account of its anatomy has been 
given. 
The distribution of this Trematode may not be confined to 
Europe, for Linton has described what appears to be the 
same or a Closely related species from an American trout 
(Salmo mykiss). No difference of specific importance is to 
be found in Linton’s description, but it is probable that the 
two forms are not quite identical (see p. 3d). 
My specimens were obtained in June, 1907, from two small 
trout captured in a tributary of the River Spey (North of 
Scotland). Hach fish contained four or five examples of the 
parasite. In another two small trout, from a stream running 
into the River Tay (April, 1907) several immature specimens 
(fig. 5) were found. ‘The intestine of one of these fish was 
absolutely crammed full of Hchinorhynchus angustatus 
Rud. while only one Distome was present. This might afford 
a striking instance of what Hausmann! terms the mutual 
crowding-out of parasites. Still another trout, of large size 
but in poor condition, was obtained later from the River Tay, 
but it contained no Trematodes. Four small trout were 
examined in May, 1908. They were also from the basin of 
the River Tay, but they did not contain Distomum 
laureatum. A few specimens, however, of Bunodera 
nodulosa (Zed.) were found in them. Olsson found the 
parasite from April to August, and Linton in July and 
August. I have had no opportunity of ascertaining whether 
it was present during the other months of the year. ‘The 
occurrence in April of immature specimens only is suggestive, 
but my material is obviously inadequate to admit of any 
conclusion with regard to the life-history. 
'<Uber Trematoden der Siisswasserfische,” ‘Revue Suisse Zool.,’ v. 
This, however, can only be regarded as an occasional occurrence except 
in particular instances. 
