16 



R. NORRIS WOLFENDEN. 



at the southernmost stations. Northwards it ranges to the west coast of Ireland, and, 

 as has been mentioned, has an extreme southern distribution. Giesbrecht's description 

 was given from only one specimen, and compared with Sars', very briefly described, 

 M. macrura. 



M. princeps, Giesbreoht. 



Cephalothorax one and a half times as long as the 



abdomen 



Anterior antennae extend beyond the furca 

 Short teeth on 1, 2, 4, 5, and 6, the 2nd the 



longest 



Genital segment longer than both the following 

 Anal segment half as long as the preceding one 

 Furca twice as long as anal, and 5 times as long as 



broad 



Size 8 '5 mm. 



M. macrura, Sars. 

 Tail about as long as the anterior division 



Longer than the body 



Only feeble traces of the strong teeth of princeps 



About as long as the two preceding segments 



5th feet like princes, but less unequal 

 Size 10-50 mm. 



Of the many examples which have come under my notice I find that the relative 

 sizes of the abdominal segments and furca are subject to some variation, thus : 



1. G.S. 30. Ab. 2, 16. Anal 6. Furca 28 long, 3 broad. Size 8 '15 mm. 



8. 25 3 8 mm. 



2. 

 3. 



4. 



28. 

 27. 

 22. 



16. 

 16. 

 11. 



7. 

 4. 



23 



12 



3 



2 



8 mm. 

 6 mm. 



The genital segment is thus always twice as long as the two succeeding segments, 

 the anal is not more than half the preceding segment, the furca is generally longer 

 than the two preceding -segments, and usually from seven to nine times longer than 

 broad. The teeth on the antennae are weak, and entirely resemble the figure given by 

 Giesbrecht in Plate 33, fig. 3 (op. cit.). 



It is difficult to resist the conclusion that the^e are one and the same species, and 

 not two different species. The male was not described by either Giesbrecht or Sars,' 

 but I have met with several examples. 



? . The largest adults were from 8-9 mm. in length. 



The body is very transparent, the head evenly rounded, cephalothorax (4 '15- 

 4 ' 5 mm. long, abdomen 4 mm. long), only slightly longer than the whole abdomen, 

 and a little over one-third as long as broad. 



The genital segment is larger than the next two, the anal not more than half 

 as long as the preceding, often much mofe than the combined length of the two 

 preceding segments and 6-9 times as long as broad, and divided into two portions 

 by the marginal bristle, of which the proximal is to the distal as 8:5. The right 

 furcal segment is sometimes a little longer than the left. Anterior antenna; at least 

 three joints longer than the furca, the basal joints broad, with short teeth on the 

 basal seven joints, of which those on the first two joints are the largest. The 



