610 GASTROPODA. [Pulmonata. 



1. Planorbis corinna, Gray, 1850. Plate 21, fig. 10. 



Planorbis corinna, Gray, P.Z.S., 1849 (1850), 167; A.M.N.H. (2), vii, 07; 

 Conch. Icon., xx, pi. 24, f. 122 ; M.N.Z.M., 32 ; T.N.Z.I., xvii, 57, pi. 12, 

 f. 6 (animal) ; Suter, T.N.Z.I., xxxvii, 252 ; J. de Conch., xli, 231 ; 

 Hedley and Suter, P.L.S. N.S.W. (2), vii, 626. 



Shell small, discoidal, periphery round, spire depressed. Sculpture 

 consisting of fine oblique growth-lines only. Colour greenish-white 

 or light brown. Epidermis thin, not or only faintly shining. Spire 

 depressed. Protoconch minute, globular. Whorls 3 to 4, slowly in- 

 creasing, the first two flat, the others gradually rising ; periphery 

 convex; base flat. Suture deep. Aperture subcircular, slightly ex- 

 cavated by the convex parietal wall. Peristome discontinuous, the 

 margins connected by a parietal callus. Basal lip advancing. 



Diameter, 4' 5 mm. ; height, 1-1 mm. (large specimen of 4 whorls). 



Animal semitransparent, greyish, minutely speckled with smoke- 

 brown. Foot short, tapering posteriorly, rounded behind and in front. 

 Rostrum emarginate. Tentacles cylindrical, rounded at the tip, widely 

 separated at the base. Eyes large, round, situated at the inner bases 

 of the tentacles. (Hutton.) 



Type in the British Museum. 



#a&. Auckland, type (Greenwood) ; ditch near Lake Takapuna ; 

 Mount St. John ; Western Springs, Auckland ; Onehunga ; Lake 

 Waikare ; Petane ; Eiver Avon, Christchurch ; Lake Wakatipu. 



Genus 2. ISIDORA, Ehrenberg. 1831. 



Isidora, Ehbg., " Symbolse Physicae," 1831. Type : Physa contorta, Mich. 

 Bulinus (Adanson) and Bullinus of authors. Diastropha, Gray, 1840. 

 Ameria, H. Adams, 1861. Glyptophysa, Crosse, 1872. Pyrgophysa, 

 Crosse, 1879. Physastra, Tapparone Canefri, 1883. 



Animal without the produced and reflected mantle-lobes of Physa ; 

 radula approaching Planorbis rather than Limnora; central tooth 

 bicuspid, cusps rather blunt, base square ; laterals tricuspid, from 

 6 to 10 ; marginals serrate, numbering 25 to 33. Number of rows 

 varying between 140 and 220. Jaw as in Planorbis. 



Shell sinistral, resembling that of Physa, acuminated or gibbous, 

 smooth or keeled ; texture somewhat thick, covered with a deciduous 

 epidermis ; columella strong ; inner lip often reflected ; umbilicus 

 sometimes wide and deep. 



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

 New Caledonia, Fiji, Tonga, Africa (except most of the eastern part), 

 southern France, Spain, and all countries bordering the Mediterranean. 



Fu.wil. The genus first appears in the Jurassic. 



KEY TO SPECIES. 



A. Shell spirally punctate lirate ; fusiform ; height of spire a 



little less" than half that of the aperture . . . . lirala. 



