.-\mphipeplea. \ GASTROPODA. 609 



part of the shell. Suture moderate. Aperture large, ovate, broadly 

 jingled above. Outer lip convex, thin and sharp. Basal lip narrowly 

 rounded. Columella arcuate, with a well-marked spiral fold. Inner 

 lip rather broadly reflexed, thin and white, covering the umbilical 

 area, and spreading over the flattish parietal wall. 



Diameter. 4-5 mm. ; height. 7-5 mm. : aperture, 4-25 mm. by 

 ft mm. (type). 



Animal olive-brown, sparingly speckled with yellowish- white. 

 Edge of the mantle simple, slightly reflected over the shell. Foot 

 broad and rounded behind ; tentacles short, flat, triangular, with the 

 eyes at the inner bases. 



Dentition (Hutton, I.e., 54, pi. 12. f. 10 ; Suter, T.N.Z.I.. xxxvii, 

 251, f. 11-14). Central tooth with 1 or 2 small denticles; laterals 

 with 3 cutting-points ; marginals with 3 to 4 denticles. 



Ova attached to stones or water-plants in gelatinous lumps of 

 10-20 together. 



Type in the Canterbury Museum, Christ-church. 



1 1 nb. River Avon, Christchurch (type) ; Lake Takapuna ; Lake 

 Waikare ; Lake Taupo, in 20 ft. to 80 ft. ; Lake Wakatipu. in 200 ft. 

 to 300 ft., also in 30 ft, to 60 ft. 



Fam. PLANORBIDffi, Adams. 



Animal having the visceral mass sinistrally coiled ; inferior pallia! 

 lobe very prominent, and transformed into a branchia ; tentacles 

 tapering. 



Shell sinistral, discoidal, usually consisting of many slowly increasing 

 whorls. 



Distribution. World-wide. 



Genus 1. PLANORBIS (Geoftroy), 0. F. Miiller, 1774. 



Planorbis, Geoffrey, Traite Coq., 1767, 12 ; Miiller, Verm., ii, 1774, 152. 

 Type : Helix cornea, L. Helix, Linne (in part). Angarius, Martini, 1773. 

 Orbis, Schroter, 1776. Nautilus, Lightfoot, 1786. 



Animal elongated, slender ; mantle with a thickened margin ; 

 foot short, truncated in front, rounded behind. Tentacles long, fili- 

 form. Jaw consisting of 3 parts. Central tooth of radula bicuspidate, 

 laterals with 3 cusps, and marginals serrate. Genital orifices distant. 



Shell sinistral, more or less discoidal ; spire flat, depressed on one 

 or both sides ; whorls slowly increasing, all of them visible from both 

 sides ; aperture small ; peristome sharp, continuous. 



Distribution. Universal . 



Fossil from the Jurassic. 



These molluscs live mostly in tranquil fresh water with an abund- 

 ance of plants in it, especially swamps ; they are rarer in flowing 

 water and the larger lakes. They have been found at altitudes of 

 12,000 ft. 



20 Moll. N.Z. 



