BIGELOW: MEDUSAE FROM THE MALDIVE ISLANDS. 249 
three is to be explained on the ground ‘that they all belong to the char- 
acteristic ‘‘ coral reef” type. Evidence that this cannot be considered a 
truly representative tropical type is found in the fact that the Canaries 
in the tropical Atlantic, whose physical characteristics, apart from the 
temperature of the water, are very different from those of any of the 
three other areas already considered, possess a Medusa fauna of mark- 
edly different characters. 
As I have already stated, all of the Leptoline Hydromedusae from the 
Maldives, with one possible exception, are new. At the same time all 
of the Trachylinae which belong to the families Geryonidae and Pegan- 
thidae, whose members are well known to be local in their distribution, 
are also new. In other words, all the ‘‘local” forms, with one possible 
exception, are new, and the only species of Hydromedusae already known 
are those distributed, or at least represented, by exceedingly close allies 
throughout the tropical oceans of the globe. This same rule holds 
good for the Discomedusae, Aurelia, and Nausithoe, the Siphonophores 
and Ctenophores. We reasonably expect to find traces of such a condi- 
tion in almost any region. The striking thing in the Maldives is the 
extent to which it is seen; for not only do we find nearly all the local 
forms new, but we find them separated from their nearest allies by very 
considerable divergences which amount often nearly to generic impor- 
tance. The frequent occurrence in the Maldives of very aberrant species 
in genera which until now have been very homogeneous is a striking 
feature. The main conclusions which I wish to draw from these facts 
are two:—first, the very large proportion of new forms among those 
groups whose members are known to be of somewhat local distribution, 
particularly the Leptolina, and the fact that none of the typical Atlantic 
or Pacific Leptolina were found, points to the conclusion that, so far as 
the Medusa fauna is concerned, the Maldives are an area of geographic 
isolation. ‘The very considerable degree of divergence from their near 
allies shown by the new species, and the frequent occurrence of aberrant 
members in otherwise very homogeneous genera, points to the second 
important conclusion, that this condition of isolation has lasted for a 
considerable period. 
The fact that all but one of the genera of Acalephs found in the 
Maldives occur in the Atlantic, while only about two thirds of them are 
known to occur in the Pacific; and that while we found no typically 
Pacific genus, we did take five genera not previously recorded, except 
- from the Atlantic, — seems to point to a closer connection with the Atlan- 
tic than with the Pacific. This connection, if it exists, is of very great 
