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, Giesbrecht. 
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 
? 
p 
About as long as the two preceding segments 
5th feet like princeps, 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 :— 
30. 
Ab. 2, 16. 
Anal 
6. 
Furca 
28 
long, 3 
broad. 
Size 8 • 15 mm. 
28. 
„ 16. 
? 5 
8. 
5 J 
25 
„ 3 
5 5 
,, 8 mm. 
27. 
„ 16. 
5? 
7. 
5 5 
23 
,, 3 
?? 
,, 8 mm. 
99 
„ lb 
5? 
4. 
12 
„ 2 
,, 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 these 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 - 0 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 more 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 
furc-al segment is sometimes a little longer than the left. Anterior antennae 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 
