984 PELECYPODA. [Eulamellibranchia. 



valves, smaller in the right valve ; the right portion of the escutcheon 

 somewhat overlapping but not hiding the deeply sunken ligament ; 

 inner margins finely crenate ; pallial sinus small, triangular ; anterior 

 right and posterior left cardinals slender, laminar, entire, the others 

 grooved or bifid, a minute pustular anterior lateral present in the 

 left valve. (Ball.) 



The New Zealand species assigned to this subgenus have an obscure 

 escutcheon, and its right portion is not overlapping. They may be 

 considered to form a distinct section. 



KEY TO SPECIES. 



A. Lunule short, cordate, broad crebra. 



B. Lunule oblong, ovato-cordate. 



a. Concentric lamella? thin and sharp, erect . . oblonya. 



b. Concentric lamella? solid, broad, adpressed subsulcatr/. 



1. Cytherea creba, Hutton, 1873. Plate 61, fig. 1. 



Chione crebra, Hutton, C.M.M., 70; Index, 89. Venus crebra, Hutton. 

 J. de Conch., xxvi, 49 ; M.N.Z.M., 147 ; P.L.S. N.S.W., ix, 522. 



Shell moderately large, ovato-cordiform, subtrigonal, thick, swollen, 

 concentrically lamellated, light brown with radiate streaks of fulvous 

 descending from the umbones. Beaks approximate, swollen, turned 

 inwards and forwards, sharply pointed, situate a little in front of the 

 anterior fourth. Anterior end short, regularly convex, the dorsal 

 margin nearly straight, rapidly descending. Posterior end subtruncate, 

 the dorsal margin lightly convex, long, slowly descending, and sub- 

 angled on meeting the posterior margin ; ventral margin regularly 

 broadly rounded. Lunule cordate, short and broad, defined by a 

 narrow groove, keeled at the middle, striate. Escutcheon ill defined, 

 sometimes marked by oblique fulvous streaks. Sculpture consisting 

 of rather distant sharp but not very high concentric lamellae, raised 

 somewhat near the margins, the interstices with a few fine growth- 

 lines ; very fine radiate lines descend from the beaks, getting much 

 more prominent on the anterior end and crenulate the concentric 

 lamellfe. Colour light brown or yellowish-white, with fulvous streaks 

 and blotches on the upper and posterior parts of the valves. Interior 

 white, porcellanous, smooth, dull. Margins very finely crenate inside. 

 Hinge-plate strong, but rather short, excavated behind the beaks ; 

 right valve with 3 cardinals, the anterior short, fairly stout, oblique ; 

 the second a little longer, subvertical, high, lightly grooved ; the third 

 longer, oblique, subparallel to the dorsal margin, grooved ; a small pit 

 in front of the cardinals ; left valve with 3 cardinals, the anterior 

 vertical, short, solid ; the second oblique, a little longer and stouter, 

 deeply grooved ; the third tooth almost horizontal, long and thin, 

 sharp ; in front there is a distinct tubercular lateral tooth. Ligament 

 deep, externally visible, with a strong inner resilium. Adductor- scars 



