161 
Report on the Mollusca collected by Mr. Herbert 
Basedow on the3South Australian Government 
North-west Expedition, 1903. 
By Charles Hedt>ey. 
[Communicated by Herbert Basedow.] 
Plate XXX. 
[Read April 4, 1905.] 
The Eremian Region has been shown by the investiga- 
tions of the Horn Expedition to possess a considerable and 
varied snail population. Desert influence has left its stamp 
on the larger snail shells. Though quite unrelated to the 
forms that people the arid regions of Asia, Africa, or 
America, these Australian shells repeat in their chalky tex- 
ture and rough sculpture the features of foreign species sub- 
jected to similar environment. 
The collection which Mr. Basedow kindly invited me to 
examine has both added to the list of known forms and en- 
larged the range of those previously described. 
I am indebted to Dr. J. C. Verco for an opportunity of 
examining the types of several species described bv the late 
Professor R. Tat'e. 
Mr. Basedow has generously deposited in the Australian 
Museum the collection here discussed. 
Diplodon wilsonii, Lea. 
For bibliography see Simpson, Proc. U.S. Nat. Museum 
xxii., 1900, p. 893. 
TJdh. — Algebuckinna Waterhole and Warrungudinn^ 
Waterhole, in the bed of the Alberga River. 
Isidora newcombi, Adams & Angas. 
For a discussion of this Eremian species, see Tate, Rep. 
Horn. Exped. ii.. Zool., 1896, p. 213. 
Hah. — Day's Gully and Hector Pass, Mann Ranges ; Tn- 
dulkanna Creek, Warrungudinna Waterhole, on the Alberga. 
Thersites basedowi, n. sp. 
Plate xxx., figs. 1, 2, 3. 
Shell discoidal, of thin and light substance, spire almost 
flat, umbilicus broad and shallow. Colour buff. Whorls 
four, parted by sharply impressed sutures. Last whorl 
acutely keeled at the periphery, rising at the last half -turn 
above the level of the coil, previous to plunging deeply below 
it, freed at the aperture from the adjoining whorl. Sculp- 
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