396 Mr. W. F. de Vismes Kane on 
general structure with those of the adult male of MM. oculata, 
correspond more closely with those of its immature form. 
But the most salient differential character is that of the 
incision or indent at the distal extremity of the telson, the 
contour of which Sars points out as also indicative of a 
slightly arrested development in JM. relicta, since it accords 
closely with the shape of the younger specimens of the marine 
species. ‘This character, though persistent in the freshwater 
species wherever taken (since Kessler’s illustration from Lake 
Onega specimens appears only to be diagrammatic), presents 
some shades of variation. Czerniavski describes the Russian 
form thus, which accords well with Sars’s plates of Scandi- 
navian specimens :—‘‘ Telsonte utrimque spinis modo 17-19 
armato, incisura postica duplo breviore et lata, marginibus 
modo leviter convexis.”” But he mentions that it varies 
somewhat, and gives two varieties—forma major, Sars, from 
Lake Ladoga, and forma orientalis, from Lakes Onega, Putko, 
and Keno. The latter is considerably the largest race of 
M. relicta known, being from 18°38 to 21 millim. in body 
length and 22°5 to 25 millim. over all, measured from the 
end of the telson and uropods to the extremity of the second 
antennal lamine. Among other differential characters he 
points out that in var. mazor the telson is armed with twenty 
spines and its feet are slender &c., with the extremity of the 
tarsus much shorter proportionally than that of var. orientalis, 
whose feet are proportionally more robust. Drs. Samter and 
Weltner, ina recently published paper, describe another form 
ot M. relicta taken by them in the Madt' Lake, Pomerania, 
which is only from 11 to 14 millim. in length as compared 
with those of Lovén and Sars, @. e. 20 and 18 millim. respec- 
tively. This form, though small, is stated to be in some 
respects nearer to M. oculata than the typical M. relicta of 
Lovén, as regards the cephalothorax and eye, and in the 
male the secondary antenne and the third and fourth pair of 
pleopods. 
Irish specimens present, so far as I am able to judge, no 
differential characters from the type of any great importance. 
Adult examples from Lough Erne, taken on the 30th No- 
vember, measured 163 millim. in body length and 22 millim. 
over all from the extremity of the antennal scale to the end 
of the telson and uropods*. ‘The telson of all the specimens 
examined was armed with twenty-two spines counting the 
terminal ones, thus differing from those of Czerniavski, and 
* These were preserved in water and formaline, whereas the quoted 
measurements of continental examples (if from spirit) would show diver- 
gence through shrinkage of the soft parts. 
