Myodora.} PELECYPODA. 1027 



C. Shell trigonally ovate or rounded. 



a. Shell equilateral, roundly trigonal ; right valve very con- 

 vex ; posterior dorsal margin almost straight . . rotundata. 



aa. Anterior end shorter, ovate-triangular ; posterior dorsal 

 margin slightly concave ; interior with 1 radial ray 

 in front of the pallial sinus . . . . . . striata. 



aaa. Anterior end a little longer ; ovate triangular ; pos- 

 terior dorsal margin lightly convex ; interior with 1 

 radial ray at the anterior end of the pallial sinus in 

 rifht valve, a little distant from it in left valve . . subrostrata. 



o 



1. Myodora antipodum, E. A. Smith, 1880. Plate 55, figs. 10, a. 



Myodora antipodum, E. A. Smith, P.Z.S., 1880, 585, pi. 53, f. 7 ; Hutton, 

 ' P.L.S. N.S.W., ix, 516 ; Index, 88. 



Shell transversely elongate, broadly truncated behind, the hinder 

 dorsal slope longer than the anterior, inequilateral, concentrically 

 ribbed, with a posterior oblique ridge on the right valve. Beaks 

 small, not much raised, acute, directed backwards. Anterior end 

 slightly shorter, acuminately curved, the dorsal margin lightly convex, 

 oblique ; posterior end broadly truncated, the dorsal margin feebly 

 incurved and slightly oblique ; basal margin regularly arcuate. 

 Sculpture of right valve consisting of concentric rather coarse lirse, 

 thickest near the anterior side and more flattened posteriorly, crossed 

 by fine and close microscopic striae ; a slightly raised ridge runs from 

 the umbo to the lower end of the truncation ; left valve very slightly 

 concave or flat, with very low and broad concentric riblets, stronger 

 at the anterior end, and fine radial lines. Epidermis thin, brown, 

 persistent usually only at the margins. Colour white where devoid 

 of epidermis. Interior white, pearly, with a single ray, curving from 

 the umbones to the lateral boundary of the pallial sinus. Margins 

 smooth, thin. Hinge with a small central triangular resilium, and a 

 small lithodesma below it. Adductor-scars subequal, roundish. Pallial 

 sinus broad, not deep, narrowly convex in front. 



Length, 13-3 mm. ; height, 9mm.; diameter, 2mm. (type). 



Type in the British Museum. 



Hob. New Zealand (Colonel Bolton). Off Great Barrier Island, 

 in 110 fathoms ; near Cuvier Island, in 37 fathoms ; Dusky Sound, 

 in 12 to 30 fathoms (Captain Bollons). North of the Auckland Islands, 

 in 85 fathoms (E. R. Waite). 



Fossil in the Pliocene. 



2. Myodora Boltoni, E. A. Smith, 1880. Plate 55, figs. 11, a. 



Myodora Boltoni, E. A. Smith, P.Z.S., 1880, 585, pi. 53, f. 9 ; Hutton, P.L.S. 



N.S.W., ix, 517 ; Index, 88. 



Shell small, transversely elongated, much narrowed posteriorly, 

 and obliquely truncated, inequilateral, the right valve moderately 

 convex, concentrically striated, thin, white. Beaks slightly raised, 

 very acute, directed backward. Anterior end a little longer, angularly 



33* 



