184 
HORN EXPEDITION—MOLLUSCA. 
The four species of A7tgasella make a relatively large addition to that section 
which is entirely confined to the Ereniian region;* from this centre there radiate 
cyrtopleura to the south of Lake Eyre and to the Great Australian Bight, 
phillipsiana to the south of Lake Eyre, flligophura to the Great Bight, and 
gascoynensis to the Gascoyne district in West Australia. Though It is noteworthy 
that the central portion of the Eremian i-egion is almost devoid of land mollusca, 
the few species within its boundaries are restricted to the limited, elevated tracts 
to the westward of Lake Eyre. 
Badistes pei-mfiata and B. fodhialis may also be regarded as endemic, having 
outliers in the southern parts of the Eremian region in South Australia and West 
Australia. The EndodoiitiB and Flamtuuliiia belong to genera largely Tasmanian, 
whilst the few continental representativ'es belong to the cooler and moister coastal 
tracts of southern and eastern Australia. The Pup(^ and Stenogyra, either by 
identical or representative species, are also largely coastal in habitat and chiefly 
Pacific in origin. The species of Ltpnrus and Succinea are also insular I’epre- 
sentatives of coastal species. 
There is every reason for the opinion that the elevated parts of the Lara- 
pintine region have been land-surfaces from pre-Cretaceous times, and that great 
climatic extremes have prevailed since that period. During the deposition of the 
Rolling Downs formation (Lower Cretaceous) this area was one of the insular 
masses constituting the archipelago to which Australia was then reduced. At this 
period a more or less cosmopolitan fauna and flora prevailed, and it was doubtlessly 
then that the Larapintine area acquired its species of Allcrophyura, Charopa, and 
Fla7nmulma, and those species of a more or less maritime habitat belonging to 
Liparus, Ste7iogyra, Pupa, and Sticcmea. How else is it possible to account for the 
presence of about eight species of land snails in the very centre of the continent, 
alisolutely isolated from allied or identical species, which are to-day circumferential 
in their occurrences ? The insularity of its geographic position was partially 
maintained during the deposition of the Desert Sandstone (Upper Cretaceous)—a 
fresh water area, or largely so, replacing the maritime one. Favourable climatic 
conditions ensued in Pliocene times, which permitted migi’ation over the largely 
reclaimed lacustrine areas. It was then that Badistes pe7-i7ijlata and B. fodmalis 
spread south and south-west; so also the A7igaselI(B, but under new modifications; 
whilst there may have been received a few northern types out of which have been 
evolved Badistes gra7iditubercuiata, B. wattii, Chloritis squa77mlosa, Thersites 
* See Aust. Assoe. Adv. Sc., Vol. i., p. 315, 1887. 
