Mytilus edulis L., Pecten vitreus Ch. and if other Ant- 
arctic regions are included the follownig species must 
be added to the above: Keliella suborbicularis Me., Scis- 
surella crispata Flem., Natica groenlandica Beck, Den- 
talium cntalis L. This list, which could be greatly 
enlarged if we included species of wide though not 
distinctly bipolar distribution, is composed almost wholly 
of species that have a wide yes universal distribution. 
Many of these doubtless found their way from pole to 
pole through the cold strata of the deepsea. To get an idea 
of the extent of such supposed migration to the Magellan 
fauna T examined Norman's list of the North Atlantic 
species of Molluses that occur below the 2000 M. line 
and found that out of 202 such species, 4 of the Magellan 
fauna occured, that is only 2°. These are, besides the 
two above mentioned widely di-tributed species of Saxi- 
cavaand Scissurella, Keliella miliaris Phil. and Puncturella 
noachina L. 
Real bipolar species do, therefore, not exist apd the 
same may be said of those genera which belong to these 
high latitudes since they are usually also represented 
by a number of species in the Temperate zone or the 
Tropics. There are Antarctic genera such as Photinula, 
Struthiolaria, Modiolarca which are not represented in 
the Arctic fauna; and vice versa, Arctic genera such as 
Volutharpa Buccinopsis, Lacuna, Moelleria, Cyprina, Mya 
etc. are wanting in the Antarctic fauna. Many genera, like 
Buccinum, Sipho, Margarita, Astarte, Cardium which are 
such important factors in the Arctic fauna are meagerly 
represented, often by only cne or two species, in the 
Antarctic region. Many genera of wide distribution (Che- 
nopus, Bulla, Anomia) enter the polar zone of the 
northern hemisphere only, and similarly others (Monoce- 
ros, Bullia, Ranella, Marginelia, Fissurella) enter that of 
the southern hemisphere only. We must, therefore, guard 
against overrating the analogy existing between the two 
circumpolar faunas. 
ae SS 
