re 
12 
known that Lake Baikal in Siberia distinguishes itself in a 
quite remarkable manner from the other Asiatic lakes by its 
astonishing richness in various species of Gammarid Amphipoda. 
It is impossible to explain this peculiarity of Lake Baikal without 
assuming that ‘a divergent development from one or a few 
ancestral forms has taken place here. 
we meet with a quite similar case, not only in the Amphi- 
poda, but also in other groups of Crustacea, viz. Mysidee, Cumacea, 
Polyphemide, as is shown by the present author in his several 
PROF. G. 0. SARS ON THE COPEPODA [Jan. 12, 
papers on the Carcinological Fauna of that interesting basin. 
Fic. 
Fig. 
Wig. 
18. 
19. 
20. 
PAE 
22. 
2: 
24. 
5. GY 
g@. Zo. 
26. 
27. 
28. 
29. 
30. 
21. 
29 
EXPLANATION OF THE PLATES. 
PrarE VI. 
Diaptomus galeboides G. O. Sars. 
. Adult, ovigerous female, dorsal view. 
. Same, viewed from left side. 
Urosome together with part’ of metasome, more highly magnified 
and viewed from the dorsal face. 
. Right lateral corner of last segment of metasome, still more highly 
c t= ? > J 
magnified. 
. Leg of last pair. 
. Adult male, dorsal view. 
. Terminal section of right anterior antenna. 
. Last pair of legs. 
Prare VII. 
Diaptonmus mivtus GO. Sars. 
. Adult female, dorsal view. 
. Same, viewed from left side. 
. Posterior part of metasome and genital segment, dorsal view. 
2. Leg of last pair. 
. Adult male, dorsal view. 
. Middle and terminal sections of right anterior antenna. 
. End of terminal part of same antenna, more highly magnified. 
. Last pair of legs. 
Projection of the 2nd basal jomt of right leg, more highly magnified. 
Prate VIII. 
Diaptomus stuhimanni Mrazek. 
Adult ovigerous female, dorsal view. 
Same, viewed from left side. 
Left lateral part of last segment of metasome. 
Leg of last pair. 
Terminal part of right anterior antenna in male. 
. Last pair of legs of same. 
Outer ramus of left leg, viewed from the anterior face, more highly mag- 
nified. 
Diaptomus simplex G. O. Sars. 
Adult ovigerous female, dorsal view. 
Same, viewed from left side. 
Urosome together with posterior part of metasome, dorsal view. 
Right lateral part of last segment of metasome, somewhat more maguificd, 
Leg of last pair. 
Outer three joints of right anterior antenna of male. 
Last pair of legs of same. 
Outer ramus of left leg, viewed from the anterior face, and more highly 
magnified. 
In the Caspian Sea, too, 
