OF THE ENGLISH LAKE DISTRICT. 431 
America have the auteiiiia! slightly longer. In the Miilaren race, which is 
one o£ the most primitive forms, the antennae in the female may reach to the 
base of the f urea. 
(3) Tlie length of the furcal rami in proportion to the whole body differs 
in different lakes, but the published information on this point is too scanty 
to admit of a definite conclusion as to whether there is any connection 
between the shortness of the furca and the length of sojourn in fresh water. 
The furcal rami of the Ennerdale and the American forms are notably 
shorter than those of the grimaldii form from the Caspian, but, on the other 
hand, both the Malaren and the Insjon races have these rami as long as or 
longer than those of my Caspian specimens. 
(4) The pointed triangular form of the lateral expansion of the last thoracic 
segment has been given by Prof. Sars as one of the distinctive characters of 
L. grimaldii, since in all the fresh-water races this segment is sim[ily rounded. 
I find in my Caspian Sea specimens that this segment is produced laterally 
into a very well-defined point (PL 23. fig. 5), and it is important to note that 
a similar point is to be found in some of the specimens from G-reen Lake and 
from Lake Canandaigua, and very rarely also in those from Lake Erie, 
while the Ennerdale race has the segment simply rounded. This character, 
small as it may appear, seems to be of importance in indicating relationship 
with the parent form, and the North American race must for this reason also 
be regarded as of comparatively recent origin. The primitive Malaren race 
has this segment generally very slightly angular, and occasionally there is a 
definite point as in L. grimaldii (PI. 23. fig. 8). 
It is remarkable that, in spite of the considerable differences in general 
body-form between the brackish and fresh-water races of Limnocalanus, 
there is no appreciable difference to be found between any of the appendages 
of the two forms, except as regards the length of the antennules. I have 
compared the appendages of the seven races available to me, and find the 
agreement perfect in almost every detail. There is, however, one very slight 
difference which may be peculiar to the Caspian race, namely the absence of 
a spine on the outer distal angle of the first joint of the exopodite in the 
right fifth foot of the male. Prof. Sars does not figure a spine in this 
position, neither was it present in a specimen examined by me, but it is 
present in all other races of which figures are published. 
Having dealt, so far as I am able, with the biology and structure of the 
Ennerdale and North American races of Limnocalanus in comparison with 
others, there remains the consideration of the question as to whether these 
races can be regarded as " relicts " in the same sense as those of the Baltic 
area. 
It must be admitted that in neither case can any definite answer be given. 
There can be little doubt that the whole of the Lakeland area was 
completely covered by ice during the Glacial period, though the view that 
