Dipludnn.] PELECYPODA. !39 



under the beaks, where there are several deep small dorsal scars. 

 Hinge : Right valve with compressed pseudo-cardinals, the anterior 

 upper tooth is small, grooved, the posterior tooth much larger and 

 crenate ; the lateral tooth is slightly arched and rugose posteriorly ; 

 left valve with the anterior pseudo-cardinal compressed, linguiform, 

 slightly rugose, the posterior subtriangular, deeply denticulate ; the 

 laterals are of nearly equal height and crenate posteriorly. Ligament 

 moderately long, strong. Adductor-scars : The anterior small, round, 

 deep ; the posterior larger, ovate, not impressed. Pallial line simple. 



Length, 51 mm. ; height, 30 mm. ; diameter, 14-5 mm. 



Hob. Lake Wakatipu. in 10ft. to 30ft. (Lucas and Hodgkin). 

 The type is from New South Wales. 



2. Diplodon lutulentus, Gould, 1850. Plate 59. tig. 2. 



Vnio lutulentus, Gould, P. Bost. S.N.H., iii, 1850, 295 ; U.S. Expl. Exp., 

 xii, 1852, 428, f. 542 ; Conch. Icon., xvi, 1865, pi. 25, f. 122 ; M.N.Z.M., 

 161 ; Medley and Suter, P.L.S. N.S.W. (2), vii, 663 ; Suter, J. de Conch., 

 xli, 291. Diplodon lutulentus, Gould : Simpson, Proc. U.S. Nat. Mus., 

 xxii, 1900, 892 ; Index, 91. 



Shell transversely elongated, scarcely falcate, dorsal and ventral 

 margins nearly parallel, rather solid, compressed, with a moderate 

 constriction at the ventral margin. Beaks at the anterior fourth, 

 scarcely modifying the dorsal outline by their prominence, much 

 eroded. Anterior end nearly as high as the posterior, regularly con- 

 vex ; posterior end rounded, the dorsal margin a little sloping ; basal 

 margin nearly straight. Sculpture consisting of irregular fine con- 

 centric ridges and faint indications of radiate striation. Epidermis 

 shining olive - green, pale leaf - green posteriorly. Interior : Nacre 

 bluish -white, with livid stains near the hinge, and a silvery brillance 

 posteriorly. Hinge with a single elongated, slightly prominent, 

 obtuse, very oblique cardinal tooth in each valve ; lateral teeth 

 slender, sharp, nearly straight, well developed, double in the left 

 valve. The limbus, outside of the pallial impression, is much thick- 

 ened. (Gould.) 



Length, 51 rnm. ; height, 25 mm. ; diameter, 10-5 mm. (type). 



Animal having the foot slaty- white, edge of the mantle and gills 

 orange ; siphonal fringes black ; abdominal mass bright ochreous- 

 yellow. (Gould.) 



Type in the U.S. Nat. Museum, Washington ; and a co-type in my 

 collection. 



Hob. New Zealand, common (Drayton). Otaua River, Hokianga ; 

 Collingwood. 



Remarks. It is not fragile, and the peculiar waves along its slope, 

 the scattered corrugations at its disc, and its peculiar colour are its 

 best diagnostic marks. These are usually concealed by a thick crust 

 of black earth. It is said to come from streams in the vicinity of 

 chalybeate springs. It varies considerably in form. (Gould.) 



