522 Mr. W. Nicoll on some 



included along with Zeugorchis acaiithus in the same genus or 

 not. This will be done with more or less readiness according 

 to the importance attached to the presence of the collar and 

 spines. As regards internal anatomy the two are well-nigh 

 identical. 



In choosing a generic name I have studiously avoided 

 reference to the spines or the circum-oral collar, so that in the 

 event of the inclusion of Distomum pittacium the name may 

 not be inappropriate. The close apposition of the testes 

 seemed to me a sufficiently diagnostic point on which to 

 found the generic name. 



Levinsenia similis {Spelolrema simile) , Jagerskiold. 

 (PI. XIII. fig. 8.) 



From the intestine and caeca of a herring-gull {Larus 

 argentatiis) considerably over a hundred examples of this 

 parasite were obtained. While they correspond closely in 

 their structure to JagerskiokFs exhaustive description * of the 

 species (as Levinsenia pygvxcea^ var. similis), yet they differ 

 slightly in one or two particulars and very much in size. 



Levinsenia joygmcea was first described as Distomum 

 pygmceum by Levinsen f from Somateria moUissima. Ac- 

 cording to him it was of very small size, its length rarely 

 exceeding "5 mm., usually much smaller. The oral sucker, 

 too, was always slightly larger than the ventral. Jagerskiold 

 later found a similar form occurring in Larus argentatus and 

 L.fuscus. The size, however, was considerably greater and the 

 oral sucker was smaller than the ventral. Tlie most striking 

 peculiarity of the species is the arrangement of the genital 

 system. The situation of the testes and ovary is not unusual, 

 but the occurrence of a large vesiculaseminalis just in front of 

 the ventral sucker and the position of the genital aperture to 

 the left of the same sucker, together with the presence of a 

 genital sinus, are diagnostic features. 



Jagerskiold compares the specimens which he found in 

 Larus with those found both by Levinsen and himself 

 in Somateria moUissima. The size of the former, as already 

 mentioned, exceeds that of the latter considerably. The 

 length of my specimens from Larus, however, shows a much 

 greater divergence. Out of about 30 examples measured, 

 none possessed a length of less than '85 mm., and many of 

 them greatly exceeded this, attaining in some cases a length 

 of 1'30 mm. The breadth of the body and the sizes of the 



* Centralbl. f. Bakt. &c. xxvii. p. 732. 



t liidra^ til Kundskab om Gronl. Treinatodfauua, p. 23, pi. iii. fig. 2. 



