1028 PELECYPODA. [Eulamellibranchin. 



rounded, the dorsal margin rectilinear and very slightly oblique ; 

 posterior end rather narrowly truncated, the dorsal margin a little 

 incurved and a trifle shorter than the other ; ventral margin convex. 

 Sculpture : The convex right valve with a raised ridge from the umbo 

 to the lower end of the truncated extremity, and with a depression 

 between it and the raised margin, the surface almost smooth, with the 

 exception of the posterior end, which is distinctly sulcated, especially 

 upon the raised ridge and the margin ; left valve somewhat concave, 

 finely concentrically striated ; both valves with very fine and dense 

 microscopic radial lines. Epidermis thin, light brown. Colour white 

 where devoid of epidermis. Interior white, pearly, with a single 

 impressed ray curving from the umbones to the upper boundary 

 of the pallia! sinus. Margins smooth, sharp. Hinge with a small 

 triangular resilium. Adductor-scars subequal. Pallial sinus rather 

 deep, extending to the vertical of the beaks, ovate, narrowly rounded 

 in front. 



Length, 14-3 mm. ; height, 9mm.; diameter, 3mm. (type). 



Type in the British Museum. 



Hob. New Zealand (Colonel Bolton). Auckland Harbour, between 

 tide-marks ; Lyttelton Harbour, in 3 fathoms (H. S.). Chatham 

 Islands. 



Fossil in the Pliocene. 



3. Myodora brevis, Sowerby, 1829. Plate 62, fig. 16. 



Pandora brevis, Sowerby, App. Stutchbury's Cat., 3, f. 2. Anatina brevis, 

 Stutchbury, Zool. Journ., v, 99, Tab. Sup., 43, f. 1, 2. Myodora brevis, 

 Hanley, Cat. Rec. Biv. Shells, 24, 338, 339, pi. 10, f. 13 ; Conch. Icon., 

 ii, pi. 1, f. 7 ; Chenu, Man. Conch., ii, 52, f. 217 ; C.M.M., 62 ; E. A. 

 Smith, P.Z.S., 1880, 580 ; Chall. Rep., xiii, 64 ; Pritchard and Gatliff, 

 P.R.S. Vic., xvi (n.s.), 101 ; Hedley, Mem. A.M., iv, 311 ; Index, 88. 

 M. plana, Reeve : Hutton, J. de Conch., xxvi, 45 ; M.N.Z.M., 137, 

 not of Reeve. 



Shell attaining a fairly large size, subtriangular, equilateral, very 

 broadly truncated behind, with sharp, rather distant, and wavy con- 

 centric lirse, fine granular sculpture, and with 2 radial posterior folds. 

 Beaks very prominent, acutely curved. Anterior end subangled, the 

 dorsal margin straight and rapidly descending ; posterior end broadly 

 truncated, the dorsal margin concave, oblique ; ventral margin broadly 

 rounded. Sculpture : The right moderately convex valve has 2 pos- 

 terior ridges descending from the umbo to the middle and the lower 

 end of the truncation, concentrically, rather distantly lirate, the 

 lirse more or less undulating, sharp, and generally more prominent 

 on the posterior folds ; the somewhat concave left valve similarly 

 sculptured, but the riblets are more feeble ; both valves are minutely, 

 very distinctly, granular. Colour white or greyish-white. Interior 

 white, pearly, with numerous radiate sulci, one deeper than the others 

 descending in front of the pallial sinus. Margins smooth. Hinge 

 with a small resilium and a falciform lithodesma. Adductor-scars 



