Introduction. 
The present publication deals with all the abundant material of marine, as well 
as land and fresh-water, mollusca that was collected during Dr. MJÖBERG'S two 
journeys to Australia in the years 191i—13. As these expeditions were directed to 
regions of Australasia of the fauna of which but little was previously known, the 
publication of their malacological results will certainly be of scientific value. The 
collections not only contain new forms, but also contribute to give a more complete 
knowledge of the distribution of the animals in question, and, further, they have 
been, as far as possible, utilized in order to increase our knowledge of the morpho- 
logy of many little studied mollusca. It is only to be regretted that in some cases 
too scanty material has been collected and that the collections are not so prolific in 
an oecological respect as they would have been if combined with information as to 
the habits and occurrence of the animals, as well as with notes on the local condi- 
tions; such accounts would have been very desirable, especially for the land mollusca. 
The marine fauna from the regions of the Indian Ocean has been the object 
of continuous research in numerous more or less comprehensive publications, and the 
literature which it is necessary to deal with in studying mollusca from these regions 
is very scattered and difficult of survey. This inconvenience is increased by the 
fact that both the descriptions and the figures given by the authors often suffer 
from many deficiences; the latter are sometimes so unsatisfactory and reproduce 
characteristics so unessential that identification is sometimes quite impossible. Some 
of the authors seem only to have had before their eyes the object of establishing a 
lot of new forms without taking pains to give them the scientific value that they 
can only acquire by careful characterization. By such neglect considerable difficulties 
are placed in the way of subsequent identification, an experience often encountered 
in dealing with the present material. When the determinations have seemed uncer- 
tain, I have given a figure of the form in question or a description of its charact- 
eristics or of the points distinguishing it from the type to which it has been referred. 
In other doubtful cases I have preferred to establish a form as new rather than 
refer it to some previously described, but insufficiently characterized, species. 
For every species of the collection I have stated not only the number of speci- 
mens collected, but also the maximum dimensions attained in each locality. By 
