HORN EXPEDITION—MOLLUSCA. 
209 
Melania balonnensis, Conrad. 
Conrad* described two Australian species of highly ornate Melaniie as 
M. tetrica and M. I>alon?tensis, and Sinithf added a third, M. suhsiniiHs. After a 
careful examination of a large series of Melaniie of this type from various parts of 
Australia, I conclude that the three so-named species are only individual modifica¬ 
tions of a highly variable one. 
AT. tetrica, which Brazier re-named M. tatei, because the species-name was 
pre-occupied by Gould, represents a shell with the subquadrate whorls having acute 
nodulations (about ten on last whorl) on the shoulder, and between which and the 
anterior suture are interposed three spiral threads. 
M. balo7in€nsis has non-angulate whorls, five or more spiral threads on the 
anterior slope, the axial costm more pronounced especially on the last whorl, 
and the peripheral coronation is almost obsolete (consisting of about twenty 
nodulations). 
These extremes of ornamentation are connectable, and few pools inhabited by 
these Melanim fail to afford the number of intermediate keels; though at the same 
time there is a tendency at each locality to develope towards one or the other 
extremes. Thus in the Cooper River at Innamincka the tetrica-iovm prevails, 
though the balon?iensis-ioYm. also occurs as well as individuals showing gradation 
of the oimament from one to the other; the converse is the case in the lower 
Murray River and in the basin of the River Finke. 
With regard to shape, the ba/o?mensis-ioYm shows a tendency to elongation, 
much more so than the tetrica-iorm, and thus in the lower River Murray, as also 
in the Finke basin, passages occur from a shell in which the proportion of length 
to breadth is 100 to 55, to one in which it is 100 to 32. This extreme elate form 
has received the name of Af. subswiilis. 
Localities .—River Finke, at Finke Gorge, at Glen of Palms and Palm Creek 
(alive), at Running Water (alive), at Crown Point; River Walker, at Tempe 
Downs (alive); River Palmer, at Illara Water. Living specimens inhabit shallow 
pools with a sandy bottom ; they often leave the water, pushing forward in the 
moist sand as a Natica on the sea-strand. This species is ovoviparous. 
* American Journ. Conchol., 1866, vol. ii., p. 80. t. 1, figs. 9, 10. 
t Journ. Lin. Soc., 1883, p. 262, t. 5, fig. 13. 
BD 
