258 Transactions. 



nating in a small point ; the lunule deeply impressed, ovate. Sculpture 

 consists of irregularly spaced, small, sharp concentric lamellations with fine 

 growth-striae in the interspaces, the lamellae as a rule become more 

 irregular as the base is approached, usually crowded in places marking 

 periods of rest ; radiate sculpture is very minute, almost absent in some 

 examples. On the posterior area of the shell is a feeble radiating flexure ; 

 the anterior dorsal area is defined by a distinct flexure, excavate aboye, 

 and the margin expanded. Marginal contour : The posterior dorsal margin 

 declining, sHghtly curved, distinctly angular on meeting the broad almost 

 uniform curve which extends around the base and terminates at the anterior 

 flexure ; anterior dorsal margin immediately in front of the umbo distinctly 

 concave, thence a well-marked rounded projection followed by a shallow 

 concavity. Interior of valves with distinct radiations ; anterior adductor- 

 scar elongated ; the posterior irregularly ovate. Hinge : Right valve 

 with two cardinals, the posterior strongest, usually bifid and a distinct pit 

 on either side ; anterior lateral, a stout rib with a small tubercule towards 

 the end ; posterior lateral simj)le : left valve with two diverging cardinals, 

 the anterior usually bifid ; anterior lateral distant, the posterior long and 

 well developed. 



Dimensions : Height, 20 mm. ; length, 22 mm. ; diameter, 13 mm. 



Locality, Nukumaru, in blue sandy clay (type) ; also Waipipi, near 

 Waverley. Collector, P. Marshall. 



Type to be presented to the Wanganui Museum. 



The Waipipi example is imjjerfect : its dimensions (approximate) — 

 height, 24 mm. ; length, 25 mm. A smaller but perfect example from 

 Nukumaru is chosen as type. 



Thracia vegrandis n. sp. (Plate XXI, figs. 5, 6, 7.) 



Shell small, fragile, oblong, inequilateral, equivalve, truncated posteriorly. 

 Beaks within the posterior third shghtly curving backwards, not prominent. 

 A blunt angular ridge extends from the beak to the basal margin of the 

 truncation ; in some examples there is a very small ridge which unites with 

 the dorsal margin of the truncation, the area thus defined is flattened and 

 somewhat excavate. Contour : Anterior dorsal margin long with a slightly 

 downward slope, almost straight, the end rounded, the curve rather narrower 

 above ; base slightly curved, almost straight, posterior dorsal margin short, 

 slightly excavate below the beak, declining more rapidly than the anterior 

 margin ; the end truncated and slightly oblique. Sculpture consists of 

 very fine concentric growth-striae, with usually a few feebly marked rest- 

 periods. The valves are slightly rubbed, and there is no indication of 

 radiate sculpture. Interior margins smooth, adductor-scars and pallial 

 line indistinct, the anterior scar the smaller, the pallial sinus aj)parently not 

 large. Hinge without teeth, deeply cleft under the apex, a comparatively 

 strong oblique and inward-projecting lithodesma posterior to the beak. 



Dimensions : Height, 8 mm. ; length, 14 mm. ; diameter (single valve), 

 2-5 mm. 



Locality, Castlecliff, blue sandy clay. Collector, P. Marshall. 



Type to be presented to the Wanganui Museum. 



The material consists of several valves. It is distinguished from 

 T. vitrea (Hutton) by its smaller size, more oblong form, the truncation 

 comparatively broader, and the less curved basal margin. 



