584 MR. E. A. SMITH ON THE GENUS MYODORA. [NoV. 16, 



15. Myodora NOVJE-ZEALANDi^, sp. nov. (Plate LIII. figs. 5, 

 5«, 5b.) 



Shell inequilateral, subequilaterally triangular ; deep valve con- 

 siderably convex, with an indistinct shallow groove posteriorly near 

 the margin, concentrically rather coarsely sulcated, the sulci ex- 

 tending from the front margin to near the posterior side, where they 

 suddenly stop, leaving a smooth narrow space between their termi- 

 nation and the edge, or, in other words, a plain posterior dorsal area. 

 The front dorsal margin is nearly straight and a trifle longer than the 

 posterior, the latter being feebly incurved ; ventral margin arcuate. 

 Interior pearly, marked with two subparallel or slightly diverging 

 rays or striae, radiating from the umbo a little beyond the centre 

 of the valve. Flat valve a trifle concave, with much finer concentric 

 sculpture than the other valve ; anterior dorsal margin straight, acute. 



Length from apex to ventral margin 8^ millims., width 9^. 



Hab. Stewart Island (C Traill) ; New Zealand. 



This species is more equilaterally triangular than any other in the 

 genus, and is remarkable for the abrupt termination of the con- 

 centric grooves on the deep valve, the smooth posterior dorsal area, 

 and particularly for the two divergent impressed rays within both of 

 of the valves radiating from the umbones as far as the pallial 

 impression. The sinus in the latter is rather deep ; and the hinder 

 muscular scar is higher up or nearer the umbo than the anterior one. 

 The shallow depression or groove proceeding down the hinder side 

 of the deep valve is near the margin, and very conspicuous. 



16. Myodora subrostrata, sp. nov. (Plate LIII. figs. 6, 6a, 

 6b, 6c.) 



Shell subtrigonally ovate, posteriorly rather acuminated and 

 scarcely truncated at the extremity, anteriorly sharply curved ; 

 ventral margin curved and feebly sinuated posteriorly, giving the 

 shell a somewhat rostrated appearance. Deep valve moderately 

 convex (in young specimens much flatter), with only a trace of a 

 shallow depression down the posterior side ; its hinder dorsal margin 

 almost rectilinear, the anterior much arcuated ; concentric sulci 

 rather coarse, generally continued to the margins. Other valve 

 quite flat, with finer sculpture. Hinge-cartilage furnished with a 

 small pellucid clavicle. Interior with a single impressed ray, 

 curving from the umbones to the sinus in the pallial impression 

 in the flat valve, and further witliin the valve in the deep one- 

 Anterior scar somewhat elongated, posterior more circular. 



Length 14J millims., width 18, diameter 5. 



Hab. New Zealand {Colonel Bolton ^' JSIus. Cuming) ; Stewart 

 Island {C. Traill). 



This species may have been confounded with M. ovata, which is 

 included by Hutton among the species of this genus said to be found 

 at New Zealand. 



M. ovata is not so narrowed posteriorly, is broadly truncated, 

 and more elongated transversely. Its sculjtture too is coarser ; and 

 the apical angle formed by the convergence of the dorsal slopes is 



