934 PELECYPODA. [Eulamellibranchia. 



2 right cardinals widely divergent and coalescent at their upper ends, 

 apparently forming one tooth ; the widening of the ventral angle 

 causes the A shape to disappear ; the nepionic shell finely concen- 

 trically striate or even nearly smooth and rather convex. 



1. Sphaerium novae-zelandiae, Deshaves. 1853. Plate 54, figs. 7, a, 6. 



Sphoeriutn novce-zelandice, Deshayes, Cat. Conch. Brit. Mus., 1853, 272 ; 

 P.Z.S., 1854, 342 ; Conch. Icon., xx, pi. 4, f. 37 ; M.N.Z.M., 154 ; Hutton, 

 T.N.Z.I., xiv, 149, pi. 2, f . E, a ; Hedley and Suter, P.L.S. N.S.W. (2), 

 vii, 664 ; Suter, J. de Conch., xli, 292 ; T.N.Z.I., xxxvii, 242, figs, in 

 text. S. lenticula, Dunker, Mai. Blatter, viii, 153. Hutton, M.N.Z.M., 

 154. Pisidium lenticula, Dunker, P.L.S. N.S.W., vii, 1883, 67. 



Shell small, ovato-trans verse, subequilateral, the anterior end 

 slightly shorter, but sometimes a little longer (in specimens examined 

 alive, with 2 siphons), compressed, shining, pellucid, yellowish to 

 light brown. Beaks approximate, flatly rounded. Anterior end with 

 the lightly convex dorsal margin descending, acutely convex towards 

 the broadly rounded basal margin ; posterior end broader, rounded. 

 Sculpture consisting of very tine concentric growth-lines and faint 

 indications of radial distant striation. Colour yellowish-white, bluish- 

 grey, or light brown. Interior bluish-white, with concentric striae. 

 Margins sharp, smooth. Hinge : Right valve with the 2 cardinal 

 teeth sometimes coalescent or in a A-shaped position, united only 

 at the top ; left valve with an upper lamellar and lower stouter car- 

 dinal tooth. Ligament small, inset, but usually distinctly visible 

 from the outside. Pallial line entire. 



Diameter Ant.-post., 6-8 ram. : dorso-ventral, 5-5 mm. : thick- 

 ness, 3-6 mm. 



Type in the British Museum. 



Hab. North Island : Lake Rotoiti, in 6 ft. : Lake Taupo, from 

 20ft. to 100ft. ; Lake Waikaremoana, from 10ft. to 20ft. (Lucas) ; 

 Lake Westmere, \Vanganui (Miss Mestayer). South Island : Birch 

 Hill Lagoon, Tasman Valley (H. S.). River Leith. Dunedin (A. 

 Hamilton) ; streams near Invercargill (Professor Chilton). Chatham 

 Islands (Professor Kirk) ; Auckland Islands (Professor Benham). 



Genus 2. CORNEOCYCLAS, Ferussac, 1818. 



Corneocyclas (in part), Ferussac, Diet. Sci. Nat., xii, 1818, 278. Type : 

 Tellina pusilla, Gmelin. Phymesoda, Pvafinesque, 1820. Pisidium, G. 

 Pfeiffer, 1821. Pern, Jenyns, 1832. Galileja, Costa, 1839. Euglcsia 

 (Leach), Gray, 1840. Cordula, Leach, 1852. Pisum, Gray; not of 

 Megerle. Cyclas, Blainville, 1824. 



Animal having an elongate foot, which is subconic, and byssiferous 

 in the young stages ; the mantle-edges free except for the anal siphon. 

 All the species are viviparous. 



.Shell small, more or less oblique, the anterior end longer than the 

 posterior, concentrically feebly sculptured ; there are no crenulations 

 of the inner margins ; lunule and escutcheon sometimes clearly 



