Rfiytida.] GASTROPODA. 771 



3 lobes. Buccal mass very large and muscular ; radula with not 

 more than 36 teeth in a transverse row. usually much less. All the 

 New Zealand species are oviparous. 



Shell umbilicated, rather thin, but not devoid of calcareous matter, 

 striated or rugose ; spire not much raised ; whorls 4 to 5, but little 

 convex ; umbilicus wide, infundibular ; peristome simple, sharp. 



Distribution. New Zealand. Tasmania, Australia. New Guinea.. 

 New Caledonia. 



KEY TO SPECIES. 



A. Periphery of body- whorl keeled. 



a. Shell thin ; periphery with a single keel. . . . . . Uunniee. 



aa. Shell solid ; periphery with a double keel . . . . duplicatn. 



B. Periphery of body-whorl convex. 



a. Shell without- microscopic spiral lines ; periphery with ~> to <i 



rounded spiral ribs . . . . . . Oreenwoodi, 



'in. Shell with distinct microscopic spiral lines. 



It. Protoconch smooth or with faint spirals ; umbilicus and 

 peristome brown ; 3 whorls ; dimensions. 1 1 mm. 

 by 6J mm. . . . . . . . . . . australis. 



bb. Protoconch radially striated. 



c. Whorls 3J ; dimensions, 11 mm. by 6| mm. . . Meesoni. 



cc. Whorls 3| to 4 ; diameter more than 12 mm. 



d. Shell with broad grooves around the periphery 

 of last whorl ; colour brown to olive ; di- 

 mensions, 23 mm. by 10 mm. . . . . patitla. 



dd. Shell without grooves around the periphery ; 

 colour pale 3 r ellow, sometimes with a brown 

 band on upper surface ; dimensions, 7f mm. 

 by 6 mm. . . . . . . . . citrii/n. 



1. Rhytida australis, Hutton, 1883. Plate 50, fig. 12. 



Rhytida australis, Hutton, T.N.Z.I., xv, 1882 (1883), 139 ; xvi, 208 : Hedley 

 and Suter, P.L.S. N.S.W. (2), vii, 631 : Suter, J. de Conch., xli, 286. 



Shell depressed, umbilicated, rather thin, translucent, malleated. 

 corneous. Sculpture of the post-embryonic whorls consists first of 

 fine radial striae which are gradually dying away but remain longest 

 at the suture, and being replaced by strongly retractive oblique plaits, 

 crossed by growth-lines and protective plaits, producing a more or 

 less malleated surface ; there are microscopic fine and dense spiral 

 lines present, sometimes faintly visible also on the protoconch, but 

 always more distinct on the base, where growth-strife predominate. 

 Colour pale horny-brown, peristome and umbilicus much darker. 

 Epidermis thin, shining on the base, dull above. Spire flatly convex, 

 very little raised. Protoconch flat, of 1J usually smooth whorls. 

 Whorls 3|, rapidly increasing, rather flattened, periphery and base 

 rounded. Suture impressed. Aperture oblique, oval. Peristome thin, 

 sharp, oblique. Columella very oblique, short. Inner lip thin, not 

 callous, broadly reflected above, and spreading as a very thin shining 

 glaze over the convex parietal wall. Umbilicus rather narrow, in- 

 fundibular, gradate, deep. 



25* 



