231 
added four other species of Aissoina (based on material supplied 
by me). The genus Rissota in one species (R. Hulliana) was 
recorded for the first time in my List of Marine Mollusca, pub- 
lished by Adcock in 1893. At that date I had in my possession 
the species herein catalogued, though their denominations had 
not then been authenticately assured, and so were not included. 
The South Australian Rissoids now number about 50; this 
very large increase is due to the dredging operations by Dr. 
Verco, whilst the denomination of a large number of the species 
results from a comparison of the Tasmanian species which have 
been !placed at my service by Mr. W. L. May (who has taken 
great pains to identify his species with the types). 
The following table, which shows the provincial distribution 
of the species, does not take into account the undescribed species 
(Rissoia, 14; Azssoina, 2) in the collection of Dr. Verco. 
| Total ) New 7 
Sp. Ss. A. | Ve i S. Ww. Q. | N. A. bey A 
Rissoia Peer” | \ 93 8 oS) Os eM yo 2 
Rissoina ... ft ee (i Ta | 7 14 LOWE Ss 16 3 
TiotaleenEgedees hy S0suby dBi. \cdTye lo tates oc tSca! eS 
The superiority of numbers in the columns for South Australia, 
Tasmania, and New South Wales is the outcome of conchological 
zeal actively and continuously pursued for the past twenty-five 
years or more ; the inferiority of numbers in the other provincial 
columns signifies, on the other hand, paucity of results rather than 
as am expression of climatic influence on the development of 
species. 
The Australian area, as a whole, compares very favourable 
in the number of its species (78) with the rest of the world. 
The sign ! suffixed to a locality name indicates that specimens 
therefrom are in my cabinet or have been studied by me. The 
incompleteness of these ‘ Contributions” arises from want of 
personal knowledge of certain species. 
As a warning note, I may allude to the tendency in the family 
to great variability of size. Employing the modified aperture as 
an index to the adult condition, which we are safe in doing so, 
because in no case have I found indications of former apertural 
modifications. J appeal by way of illustration to my measures 
of a macromorph and a micromorph of my Rissoina punctatissima, 
both with completed apertures and of the same number of whorls. 
Despite this variability in size, not actually observed in all the 
species, I do not find correspondingly therewith variations of 
sculpture, at any rate not to that extent to make specific limita- 
tions difficult to define. 
