390 Annals of the South African Museum. 



the teeth are not well preserved. The stout clavicular ridge is de- 

 cidedly curved forw^ard. The beaks are tumid, incurved, and rise 

 above the hinge-line. Owing to imperfect preservation the opposite 

 valves in this one individual have quite a different appearance, the 

 left-hand one having the ventral margin broken, and thus possessing 

 a much more oval shape than the other. 

 Locality. — Zwartberg Pass. 



NUCULITES PACATUS sp. nov. 



(PL XLVII., figs. 5, 5a, 6.) 



Shell elongated oval, one and a half times as long as high ; ends 

 regularly rounded, anterior end rather narrower and more pointed 

 than posterior end ; ventral margin strongly convex ; dorsal margin 

 weakly convex, not oblique ; greatest height of shell a little behind 

 beaks. Beaks low, obtuse, broad, directed forwards, scarcely rising 

 above hinge-line, situated rather forward, at about one-third (or 

 rather less) the length of the shell from anterior end. Valves very 

 convex, swollen, especially in umbonal region just behind and below 

 beaks. Clavicular ridge very thick and strong, nearly vertical or 

 faintly curved forwards, extending about two-thirds the height of 

 shell. Hinge-line with 8 rather long teeth of equal size radiating 

 downwards, situated on semicircular plate between clavicular ridges 

 just in front of beaks ; no teeth in front of them, but behind them a 

 straight row of 30-36 small transverse teeth, increasing gradually in 

 size posteriorly and extending about two-thirds of the distance 

 between the beaks and posterior end of shell. 



Dimensions : — I. II. 



Length 46 mm. 45 mm. 



Height 29 26 



Thickness 26 24 



Locality. — Zwartberg Pass. 



Bemarks. — The elongated oval shape of the shell, the strong con- 

 vexity of the valves, the low beaks and stout clavicular ridge are 

 distinguishing features. The good preservation of the hinge-line in 

 one specimen enables us to fix the characters of the dentition with 

 certainty. From N. hranneri it differs by the more elongated shape 

 and more swollen sides, by the more subequal ends of the shell, 

 by the lower beaks, by the non-obliquity of the dorsal margin and 

 the stronger and straighter clavicular ridge. Prom N. bcneckci var. 

 the shape of the shell at once distinguishes it. 



