COMPOSITION AND ORIGIN. 197 
light on the problems under consideration, and at the same time to avoid including 
those non-Australian forms which would be of no service. After careful sifting, 
I find 290 species, one subspecies (in Salmacis) and one variety (in Ophiocoma) 
which must be taken into account in analyzing the Torres Strait fauna. Of these, 
239 species, the 1 subspecies and the 1 variety make up that fauna, while the remain- 
ing 51 occur only on the coast of Queensland (17) or only to the west, north, or 
east of Torres Strait (33). It may be stated at once that probably many and per- 
haps all of the 17 Queensland species will be found ultimately in the Torres Strait 
region, and the same may be true of many of the 33 other species. Their apparent 
absence is due very probably to our imperfect knowledge. 
THE QUESTION OF A SOUTHERN ELEMENT. 
On examining this list, one is at once struck with the paucity of southern forms. 
There are surprisingly few species found in the Torres Strait region which occur 
south of Queensland, and nearly all of these are obviously tropical forms which 
have extended their range to Port Jackson. There are 9 species (Asterina exigua, 
Amphiodia mesopoma, Ophiactis luteomaculata, Ophiothela hadra, Pectinura arenosa, 
Laganum laganum, Thyone buccalis, Thyone okeni, Pentacta doliolum) which admit 
of a different interpretation but examination of their ranges gives little support 
to the view that they represent a southern fauna. Not one of the eight genera is 
characteristically Australian, nor is there one confined to the southern hemisphere. 
The holothurian Pentacta doliolum was originally described from the Cape of Good 
Hope, but it is recorded from a number of East Indian stations, and apparently 
occurs all around Australia. It must be granted, however, that its specific charac- 
ters are not well worked out and the various records are not of uniform reliability. 
The other holothurians, the two Thyones, are known only from the eastern coast 
of Australia and might be considered southern species which have extended their 
range to Torres Strait, but as more than half the known species of Thyone occur 
north of the equator and the nearest relative of these forms is an East Indian species 
(sacellus), that would seem to be an unnatural explanation of their distribution. 
The occurrence of Laganum laganum as far south as Tasmania is remarkable, but 
it is a common species in the East Indian region and is in no real sense a southern 
form. The brittle-star Pectinura arenosa was originally taken in Bass Strait, but 
seems to have a distribution corresponding to that of Laganum laganum, and the genus 
is certainly not a southern one. The other three brittle-stars in the list are too 
little known to use as the basis of any argument, but in view of the fact that both 
Ophiactis and Amphiodia are common tropical genera, it is difficult to believe that 
these species are indicative of a southern element in the Torres Strait fauna or on 
the Queensland coast. The sea-star Asterina exigua has a distribution which quite 
warrants the belief that it represents a southern fauna, but unfortunately for this 
view, the genus is essentially a tropical one, and since exigua is recorded from Java, 
the Moluccas, and the Philippines, it is not at all necessary to consider it a southern 
form. This absence of a southern or even a characteristically Australian element 
in the Queensland and Torres Strait fauna is somewhat disconcerting, for it brings 
