Trematode Parasites of British Birds. iCu 



specimens measured about GO per cent, showed the oral 

 sucker orieater than the ventral, but taking the average of 

 the figures obtained it was found that both approximated 

 •050 mm. The limits in each case are •043-06;^ ram. The 

 suckers are therefore very nearly equal, the oral sucker 

 being usually a little the larger. In tlie immature specimens 

 from Hcematopus and Larus ridibundus the oral sucker is 

 invariably distinctly greater. The oral sucker is subterminal 

 and the ventral sucker is almost midway l)etween the anterior 

 and posterior ends of the body. The prepharynx is usually 

 of considerable length, '002 mm. on an average, being nearly 

 twice as long as the {)harynx, which measures 033 X "OlO mm. 

 In the Hamatopus and Larus specimens the prepharynx was 

 usually much shorter. The oesophagus measures -06-16 mm., 

 being i-| of the body-length. The diverticula are more 

 than twice as long, •16-'37 mm.^ and this forms an important 

 point of difference between this species and the other two 

 species of the genus. They always extend as far back as the 

 anterior border of the testes. 



The ovary is situated immediately behind the ventral 

 sucker, median or a little to the right. The characteristic 

 triln])ate outline is well marked. The uterus is so voluminous 

 that its convolutions cannot be followed. It first fills the 

 left side, where the ova are colourless, then passes to the 

 right, where they arc yellow in colour ; the condition is 

 thus the reverse of that in Spelotrema. The numerous ova 

 measure •020-022 x •010--012 mm. The yolk-glands have 

 the situation and extent already noted in the definition of 

 the genus, and this is constant for all three species. The 

 testes are not overlapped by the uterus to any great extent, 

 so that they are probably almost as thick as the body itself. 

 Their outline is elongated oval, and their long axes are 

 directed more or less obliquely upwards towards the middle 

 line. In the specimens from Larus ridibundus the long axes 

 are directly transverse, while in those from Hceinaiupus the 

 testes are almost globular. The shape and position of the 

 tirrus-pouch have been noted in the definition of the genus. 

 The vt'sicula scminalis within the pouch had a perfectly oval 

 outline and is proportionately smaller in this species than in 

 the other two. It does not extend much further back than 

 the middle of the ovary. The terminal portion of the vagina 

 has a sinuate course. 



Marilrema lepidnm, sp. n. 



This occurred only in the intestine of Larus argeutntua. 

 It is about the same size as the previous species, but differs 



1«* 



