LAMELLIBRANCHTATA. 



diverging cardinal teeth, and usually with anterior and posterior 

 laterals ; pallial sinus short, rounded. 



MACTRA. 



Sub-equilateral, anterior hinge tooth A-shaped, sometimes with a 

 small lamina tooth close to it ; lateral teeth doubled in the right valve. 

 World-wide. 



19. M. diSCOrS, Gray. Ovato-trigonal, slightly ventricose, 

 smooth, with fine longitudinal striae ; lunule and area plicately striated ; 

 anterior side rather shorter, its dorsal line curved outwards ; posterior 

 side rather flattened, its dorsal line convex. White ; epidermis thin, 

 pale horn colour. Height, 2'5 ; length, 3. 



Common. 



* 20. M. HlUFChisoni, Desliayes. Shell ovate, sub-ventricose, 

 rather solid, white, smooth, covered towards the margin with a straw- 

 coloured epidermis, nearly equilateral, anterior side rounded, posterior 

 rather the longer, slightly angularly produced, angle linearly keeled, 

 lunule very large, wrinkle ridged, umbones close set. (Reeve.} 



21. M. SCalpellum, Deshayes. Shell triangularly oblong, thin, 

 very compressed, equilateral, smooth, shining white ; extremities rather 

 attenuately rounded, umbones very small, close ; lunule and area very 

 narrow, indistinct, plicately striated. (Reeve.} 



Much like a Tellina. 



Stewart's Island. 



* 22. M. donaciformiS, Gray. Shell ovately triangular, in- 

 equilateral, swollen, semicordate, umbones sharp, opposite, distant, 

 transversely very finely striated ; white, beneath a fulvous epidermis, 

 anteriorly obtuse, posteriorly broadly flat and angled, accuminated at 

 the extremity. (Reeve.} 



23. M. SBQUilatera, Reeve. Trigonal, nearly as high as long, 

 solid, longitudinally striated ; lunule smooth ; anterior end sub- 

 angulated, slightly flattened above, posterior angled, and flattened 

 above. White, umbones tipped with purplish ; interior yellowish, 

 sometimes purplish in the upper part. Height, 1'75 ; length, 2 25. 



Common. 



HEMIMACTRA. 



Trigonal, more or less keeled behind ; cardinal teeth moderate, 

 lateral teeth extended ; ligament triangular, sub-marginal near the 

 cartilage plate ; pallial sinus small, rounded. 



* 24. H. OVata, Gray, Dieff. N.Z., u.,p. 251. Ovato-ventricose, 

 inequilateral, thin, slightly concentrically wrinkled ; rounded in front, 

 rather attenuated and produced behind. White covered with a thin 

 pale brown periostraca, much produced beyond the edge behind ; inside 

 yellow ; lateral teeth short, very high, and sub-triangular. 



West Coast of North Island (DiefFenbach). 



