8 EDWARD T. BROWNE. 
In the collection from the Falklands there are seventeen species of Hydromeduse (for 
names, see Browne, 1902) belonging to sixteen genera. Not one of these species has 
yet been found in the Antarctic, and only two of the genera, namely, Eleutheria and 
Phialidium, are represented there. Among the Scyphomeduse the genus Desmonema 
is common to the Magellanic and Antarctic regions, but the species are distinct. 
Eleutheria charcoti, found off the Antarctic continent near Wandel Island (south of 
the Falklands), is more like E. hodgsoni from “McMurdo Sound than like £. vallentini 
from the Falklands. If we compare the Antarctic Meduse with the records (which 
are still very meagre) from Australia and New Zealand, we find that only one genus 
(Margelopsis) and no species are common to both regions. 
The recent Antarctic explorations have produced a fair number of new Medusa, 
many of which have well-marked and interesting specific characters, but there are only 
about three new genera. I expect that ultimately not one of them will remain 
peculiar to the Antarctic fauna. All the genera, except those recently described, have 
representatives in other parts of the world, frequently living under totally different 
conditions and in localities far apart. As the littoral Hydromeduse of the Antarctic 
have not yet been found in the Magellanic, South Australian, and New Zealand areas, 
it looks as if they belonged to an ancient stock which has long been isolated by the 
Great Southern Ocean from the rest of the world. 
Sir John Murray, K.C.B. (1896), says: “In water of a low temperature the 
metabolism in cold-blooded animals would be much less rapid than in water of a 
high temperature, and all those changes which result in the evolution of new species 
would proceed at a much slower rate at the poles than in the tropical belt.” If the 
Medusz of the Antarctic region have long been isolated, and their evolution has 
proceeded at a slow rate on account of the coldness of the water, then, when an Antarctic 
species is compared with another species of the same genus inhabiting warmer water 
we ought to be able to see a difference and mark the course of evolution. As evolution 
is proceeding at a much slower rate in cold than in warm regions, the characters of 
an Antarctic Medusa should be more primitive than those of one from warmer seas. 
The following are instances of this primitive condition :— 
The genus Solmundella has a very wide geographical range, extending from the 
tropics to the Antarctic. It has only two opposite perradial tentacles, and the genus 
is descended, without doubt, from a genus which had four perradial tentacles. Beneath 
the two tentacles there is always a deep groove in the wall of the umbrella. In the 
Antarctic form there is still a conspicuous groove present in the two perradii without 
tentacles. The grooves have disappeared from the two perradii without tentacles in 
the species found off Ceylon. The species from Ceylon has not only lost all traces of 
the grooves, but in addition has developed about four times the number of sense 
organs found in the Antarctic species. y 
A new species of Sibogita found in the Antarctic has only four centripetal canals, 
whereas the other species have eight or more centripetal canals. 
