38 A MONOGRAPH OF 



58. — Helix ( ) Roblixi. N. Sp. 



Shell small, deeply and narrowly umbilicate, discoid, pure white, 

 finely, very closely and regularly striated above and below, striae 

 abruptly terminating at the apical whorls (IJ to 2), which are dis- 

 tinctly spirally striate ; spire flat ; whorls 4 J, slowly increasing in size, 

 last rounded ; suture deeply excavate ; aperture roundly lunate, not 

 descending in front ; margins distant, joined by an extremely thin 

 deposit of callus ; columellar not dilated. 



Diameter, greatest 2|, least 2 ; height 1 mil. 



Habitat. — Distillery Creek, near Launceston. 



Of very rare occurrence, attached to the under surface of stones in 

 moist places. Easily known by the sudden termination of the fine striae 

 on the embryonal whorls, where it is replaced by minute spiral lines. 

 It is much more minutely sculptured than the two preceding. 



59. — Helix ( ) Barrenensis. N. Sp. 



Shell small, bi-concave, discoid, thin, regularly, somewhat closely 

 ribbed, and under the lens strongly decussate, embryonal whorl smooth, 

 horny-brown ; spire much submerged gradually ; whorls 5|^, la&t 

 rounded, base with ribs as above ; umbilicus widely open, shallow, freely 

 exposing the whorls ; aperture vertical, semi-lunar, faintly flattened 

 above; peristome simple. 



Diameter, greatest 2, least 1 J ; height 1 mil. 



Habitat. — Furneaux Group, Bass Straits (R. M. Johnston) ; Emu 

 Bay (?) — a single specimen. 



On the islands comprised in the Furneaux Group it is invariably 

 found gregarious, gathered together in shallow depressions on the sand 

 dunes with H. Furneauxensis and H. pictilis. 



Yery closely allied to H. lirata (Cox) from New South Wales, but 

 difiering in the riblets being more numerous, greater number of whorls, 

 and the spire showing greater submergence. 



60. — Helix ( ) Hookeriana — R. M. Johnston. 



Pro. R.S.T., April, 1879. 



Shell minute, planorbiform, bi-concave, somewhat openly, per- 

 spectively umbilicated ; whorls 4|, obliquely, arcuately striate, com- 

 pressed, with alternate bands of red and brown, preceding whorls sunk 

 in and closely embraced by the last, the base being rather more deeply 

 submerged and the upper surface shallower and more openly perspective; 



