Trematode Parasites of British Birds. 259 



flistinct membrane. It is situated in the long axis of the 

 body ; broad posteriorly, tapering gradually forwards. 



There is some resemblance between this species and 

 Distumum Muehlingi. They are about the same size and 

 their ova are equal, but apart from the questionable presence 

 of a genital sucker in D. MuehUngi, it displays the following 

 differences : — The outline of the body is constricted in the 

 middle ; the cesophagus is much longer ; the yolk-glands do 

 not extend in front of the ventral sucker, but are more 

 voluminous posteriorly, uniting between tlie testes, which 

 are some distance apart; the ovary is rounded; the vesicula 

 seminalis is not voluminous ; and the ova are few. 



To col rem a Ungua (Crepl.). 



1 have already frequently referred to this species and to 

 Jjigerskiold's excellent note on it ^. It is a very common 

 parasite of the iierring-gull, its favourite habitat being the 

 anterior end of the intestine, particularly the duodenum. 

 In addition a new host, Alca tarda, must be mentioned. 

 Only one bird of this species was examined, and it yielded 

 but a single example of the parasite, so that its occurrence 

 may be no more than casual. It is a small specimen abont 

 1 mm. long, with few ova, but it is undoubtedly identical with 

 the specimens from the herring-gull. 



The numerous specimens from Larus argentains show a 

 remarkable uniformity in size. The length varies from 

 1*5 mm. to 18 mm., while the maximum breadth is rather 

 less than ^ of the length, and occurs usually in the anterior 

 part of the body, giving the outline the familiar tongue- 

 shape. Occasionally the anterior part is more tapering. 

 The cuticular scales cover only the anterior part of the body, 

 but they extend somewhat further back than Jagerskiold 

 represents them. The oral sucker has a diameter of "075- 

 •085 mm., and the ventral sucker appears to be nearly of the 

 same size, although it is difficult to measure the latter owing 

 to the absence of a limiting membrane. The pharynx 

 measures "06 x *04'5 mm., and the short prepharynx is about 

 \ as long. The oesophagus is extremely short (Oi-'OG mm.), 

 being not more than Jr^ of the body-length, Jagerskiold's 

 statement that it never exceeds I of the body-length seems 

 to be an oversight, for it never in any circumstances 

 approaches near that length, and in his figure, which is quite 

 correct, it is not more than ^q. It is thus much shorter than 

 that of T. jejunum or Distomum Muehlingi. 



* Bergeus 3Ius. Aarboj.', 1898, no. ii, 



