940 PKLECYPODA. [tiulamdliljranchia. 



3. Diplodon Menziesi, Gray, 184:}. Plate o'.i, fig. 3. 



Unio M<:nzicni, (iray, Dien' X.Z.. 1843, 257; Conch. Icon., xvi, pi. 29, 

 f. 152; Hanley,' Phot. Conch., pi. 2, f. 1: .M.X.Z.M., 160; Mutton, 

 T.X.Z.T., xiv, 148, pi. 2, f. A-C ; Hedl<-\ and Suter, P.L.S. N.S.W. (2), 

 vii, 662 ; Suter, J. de Conch., xli, 290. Diplodon M< nzinsi, Cray : Simp- 

 son, Proc. U.S. Nat. Mus., xxii, 1900, 892 ; Index, 91 : Suter, T. N.Z.I., 

 xxxvii, 234. Unio n-ui/carensc, Colenso, Tasm. Jonrn. Nat. Sci., ii, 

 1845, 250 ; T.N.Z.I., xiv, 169. 



Shell oblong, high, compressed, thin, winged behind, olive-brown, 

 concentrically ridged, and often with radial elongate nodules about 

 the middle of the valves. Beaks hardly raised above the dorsal line, 

 approximate, rounded. Anterior end broadly rounded, short, angled 

 towards the straight oblique dorsal margin : posterior end long, 

 higher than the anterior, winged above, obliquely truncated, produced 

 and narrowly rounded below ; basal margin lightly convex. Sculp- 

 ture consisting of unequal, strong, concentric striae and ridges, crossed 

 by fine radiate strise ; young shells have the umbones ornamented 

 with sharp, curved ridges, but this is usually lost in the later stages 

 of growth, the beaks being much eroded ; adult specimens some- 

 times are distinctly sculptured with elongate nodules on the lower 

 tialf down to the ventral margin in the region below and behind the 

 beaks. Epidermis thin, somewhat shining. Colour olive to olive- 

 brown, young specimens light yellow or green. Interior greyish-white, 

 slightly iridescent, olive at the umbones. sometimes this colour ex- 

 tends over the greater part of the valves, radiate striation more or 

 less distinct anteriorly. Hinge very variable : right valve with 2 

 pseudo-cardinals, the inner one large, thick, ovate, rugose, the outer 

 one a small triangularly elevated lamella, the lateral tooth a long, 

 compressed, slightly arcuate lamella, slightly crenate and elevated 

 posteriorly ; left valve with the anterior pseudo-cardinal tooth stout, 

 excavated behind, the posterior tooth rudimentary, the 2 lateral 

 teeth long and slender, lightly curved, the upper one shorter, both 

 somewhat raised and crenate behind. Li</(tict external, long and 

 stout. Adductor-scars subequal. close to the ends of the hinge, the 

 anterior scar much deeper and more rounded. Pallial line simple, 

 the anterior part of the valves much thickened outside it. 



Length, 77 mm. ; height, 47 mm. ; diameter, 22 mm. 



Animal and Anatomy. Hutton, T. N.Z.I., xiv. 149, pi. 2. f. A-D. 



Type in the British Museum. 



Hob. North and South Islands, in creeks, rivers, ponds, and lakes, 

 from shallow water to a depth of 100 ft. 



Subsp. acutus, Suter, 1907. Plate 11, figs. II, Ho. 



Diplodon Menziesi acutus, Sut.. 1'. Mai. ,s.. \ii, 1907, 239, pi. 22, f. 11, 12. 



Distinguished from the species by the very distinctly rostrate 



posterior end, the nearly total absence of radial sculpture, and by 



being more compressed. Only young shells show traces of radial Iv 



arranged nodules near the beaks. The basal margin is generallv 



