942 PELECYPODA. [Eulamellibranchia. 



truncated, the dorsal margin slightly arched, descending ; ventral 

 margin straight and sinuated in the middle. Anterior part of valves 

 with distinct radiate strise. Hinge with the teeth not much de- 

 veloped ; the 2 pseudo-cardinals of the right valve lamellar, low. 

 slender, the lateral tooth a fine, long, curved lamella, raised pos- 

 teriorly ; left valve with 1 elongate oblique pseudo-cardinal, some- 

 times a second rudimentary tooth behind it ; the laterals thin, curved, 

 the upper one a little shorter. 



Length, 61 mm. ; height, 30 mm. ; diameter, 14 mm. (type). 



Type in the Dominion Museum, Wellington. 



Hob. Lake Takapuna, type (F. W. Hutton) ; Kaipara Heads. 



Subsp. Hochstetteri, Dunker, 1862. Plate 59, fig. 6. 



Unio Hochstetteri, Dunker, Mai. Blatt., viii, 1862, 153 ; Conch. Icon., xvi, 

 pi. 86, f. 463; M.N.Z.M., 161 ; Hedley and Suter, P.L.S. N.S.W., (2), 

 vii, 663. U. Menziesi Hochstetteri, Dunker : Suter, J. de Conch., xli, 

 291. Diplodon Menziesi Hochstetteri, Dunker : Simpson, Proc. U.S. 

 Nat. Mus., xxii, 1900, 889 ; Suter, T.N.Z.I., xxxvii, 237. 



Shell thickish, depressed, very inequilateral, narrow and very 

 short in front, broadly biangular, and somewhat winged behind. The 

 young shells are invariably typical I). Menziesi, but on growing larger 

 the posterior end is getting roundly or biangularly truncated ; the 

 periostracum is produced in thick foliated layers, and the inner margin 

 is considerably thickened by pearly substance, forming large rugosities, 

 and very often pearls adhering to the shell are met with. Loose 

 small pearls of irregular form are only exceptionally found. In my 

 opinion the cause of this is most likely some parasite, as is the case 

 in most of the pearl-producing bivalves. The concentric striation is 

 rather coarse, the marks of rest distinct and elevated. Right valvt 

 with 2 pseudo-cardinals, the upper anterior forming a small lamella, 

 the posterior being strong, compressed, high, triangular, and slightly 

 corrugated ; the single lateral tooth slightly curved, its posterior end 

 usually abruptly descending. Left valve with 2 pseudo-cardinals 

 arising from a common base, both blunt, the anterior larger ; the 

 2 laterals curved, the lower one denticulated posteriorly, gradually 

 descending. 



Length, 65 mm. ; height, 48 mm. ; diameter, 23 mm. 



Type in the K.K. Hofmuseum, Vienna. 



Hob. River Waikato, type (Hochstetter) ; Lakes Rotorua. 

 Rotoiti, and Taupo, to a depth of 30 ft. ; Kopuaranga River 

 Cheviot ; River Avon. 



Subsp. Lucasi, Suter, 1905. Plate 59, fig. 7. 



Diplodon Menziesi Lucasi, Suter, T. N.Z.I., xxxvii, 1904 (1905), 239, f. 2, 

 3 in text. 



Shell oblong - ovate, very much compressed, thin and fragile. 

 Beaks low, eroded. Anterior end short, angularly rounded ; posterior 

 end produced, obliquely truncated ; dorsal and ventral margins 

 slightly diverging, both straight, the latter slightly sinuate. Surface 



