524 PKOF. C. H. O DONOGHUB : EEPORT ON 
the first place, the Abrolhos Islands are probably the most southern coral- 
islands in the world'. A tropical current from the north and north-east 
passes down and bathes their shores, and the available evidence goes to show 
that the temperature of the sea round the islands is usuallj' some degrees 
higher than that near the adjacent coast — indeed, even in the winter, it rarely 
falls below 20° C. He further suggests that if a preponderance of tropical 
species is found it will probably be due to this warm current, although the 
fishes apparently are southern forms. 
Of the Tectibranchs, one (i. e., T. gigahtea) has been recorded previously 
from Queensland. The two genera Dolahrifera and Placohranclms are, 
on the whole, distinctive of tropical or sub-tropical seas, while Bertliella 
is perhaps more widely distributed. 
It may be stated of the Nudibranchs that, as a general rule, the Clado- 
hepatica are characteristic of cool or cold waters, while the Holohepatica 
characterise warmer regions. It is therefore probably not without signifi- 
cance that all the forms in the present Abrolhos material belong to the 
Holohepatica. In passing, too, it may be worth while to notice that, of the 
Cladohepatic genera recorded from the coast of the mainland of Western 
Australia, i. e., Armina (Pleuroj^hi/Hidia), Sci/llcea, and Madrella, the two 
former are of world-wide distribution and the last is a more or less tropical 
group. All other West Australian forms so recorded are Holohepatic. 
Turning again to the present material, the Sph^rostomids are universally 
distributed, but practically all the other genera are distinctly those of tropical 
and sub-tropical seas. 
Comparing this list with that of the British coast or of the northern part 
of the Pacific Coast of North America, the difference is most striking, and it 
is impossible not to recognize that it is far more sub-tropical in character. 
Cold-water groups appear to be entirely unrepresented np to the present, and 
it is hardly possible that, even if found, they will ever outnumber the tropical 
and sub-tropical genera. 
We may conclude, therefore, that, as far as the Opisthobranchs at present 
known are concenied, the fauna of the Abrolhos Islands is distinctly sub- 
tropical or tropical in its constitution. 
The remarkable way in which the ordinary usages of systematic taxonomy 
have not merely been ignored but flagrantly violated by many workers on 
Nudibranchs has created such a series of pitfalls that even with the utmost 
care it is almost impossible to avoid them all. Among the most obvious of 
these are examples where species have been given new names, apparentlj^ 
because the author did not like the previous one, and this although the older 
name has many years' priority, and the identity of the two forms is empha- 
sized. Again, several genera have been combined and a new generic name 
invented, or the reverse of this may have happened and an old genus split 
up to make way for two or more new ones, while the original name has been 
