Thcrnxta.} GASTROPODA. 651 



aceous thin plaits, about 4 per millimetre, sometimes inequidistant, 

 produced at the periphery into elongated triangular acute mem- 

 branous processes ; interstices minutely reticulated by growth and 

 spiral hues. Colour pale brown to greenish-corneous. Epidermis thin, 

 not shining. Spire conoidal. rather acute, a little higher than the 

 aperture. Protoconch of li convex whorls, mostly corroded. Whorls 

 5, firmly pressed together, the last sharply angled, not descending 

 in front ; base rather convex, impressed in the middle. Suture im- 

 pressed. Aperture oblique, subtriangularly lunar. Peristome acute, 

 with an inner thin callosity. The outer lip angled. Columella very 

 short. Inner lip oblique, callous, reflexed above and partly or entirely 

 closing the narrow perforation ; parietal wall with a thin white callus. 



Diameter Maj., 4 mm. ; min., 3| mm. : height, 2^ mm. (type). 



Dentition. Hutton, T.N.Z.I., xvi. 162, pi. 9, f. ; pi. 11. f. U. 



Jaw slightly arcuate, with flat ribs ; very delicate. 



Radula with the formula 18+1 + 18; laterals about 5. Central 

 tooth tricuspid ; laterals with a long rnesocone ; marginals bidentate, 

 the inner cutting-point large. 



Type in the British Museum. 



Hob. North Island : Whangaroa ; Whangarei ; Little. Barrier 

 Island (Adams) ; Waiheke Island (H. S.) ; Thames ; Hillyer's Creek ; 

 Birkenhead ; Mount Wellington lava-fields, near Auckland ; Hunua 

 Kange (Major Broun) ; Ohaupo (Musson) ; Mount Pirongia (T. Urqu- 

 hart) ; Tuakau (S. Bull) ; Waitakerei Range (H. S.) ; Ngaputahi, 

 Tuhoe-land (A. Hamilton) ; Ormondville ; Toko, near Stratford (R. 

 Murdoch) ; near Rotorua ; Forty-mile Bush (H. 8.). South Island : 

 Happy Valley. Canterbury (F. Suter). 



3. Therasia decidua, Pfeifier, 1857. Plate 50, fig. 8. 



Helix decidua, Pfr., P.Z.S., 1857, 108 ; M.H. Viv., iv, 71 ; Hector, Cat. 

 Land Moll. N.Z., 9. Patula (Charopa) decidua, Pfr., Nomencl. Hel. Viv., 

 97. P. decidua, Pfr. : Hutton, M.N.Z.M., 6. Therasia decidua, Pfr. : 

 Hutton, T. N.Z.I., xvi, 203. Gerontia (Therasia) decidua, Pfr. : Pilsbry, 

 Man. Conch. (2), viii, 71, pi. 22, f. 52-54. Therasia decidua, Pfr. : 

 Hedley and Suter, P.L.S. N.S.W. (2), vii, 041. Flammulina (Therasia) 

 decidua, Pfr. : Suter, J. de Conch., xli, 245 ; Man. Conch. (2), ix, 16. 



Shell depressed, subglobose, thin and fragile, narrowly umbilicated. 

 Sculpture : Protoconch microscopically spirally striate. the succeeding 

 whorls with membranaceous deciduous fine riblets. 3 to 4 per milli- 

 metre ; they are oblique, retractive, flexuous, and somewhat inequi- 

 distant ; very often these riblets are altogether absent, fine growth- 

 lines taking their place ; interstices with fine growth -lines and minute 

 spiral liree. Colour brownish-horny, with reddish streaks following the 

 direction of the riblets and extending over the base ; very often there 

 are only faint or no colour-markings. Epidermis thin, subtranslucent, 

 faintly shining or dull. Spire low conoidal, apex blunt, outlines 

 lightly convex, the height very little more than half that of the aper- 

 ture. Protoconch of 1| convex whorls, the nucleus slightly raised. 



