Plaxiphora.] AMPHINEURA. 



with fine diverging striae, which are coarser near the anterior margin 

 and form elongated nodules on the posterior margin. Intermediate 

 valves with a lighter-coloured posterior mucro, the whole surface 

 sculptured with fine striae ; the lateral areas distinctly marked off 

 by an elevated ridge descending from the mucro and dissolving into 

 numerous fine striae, the striae of the lateral and central areas radiate 

 from that ridge like the webs from the shaft of a feather ; sutures. 

 with a row of nodules ; central areas with diverging riblets on the 

 jugum, but straight and parallel to the jugum on the sides. Pos- 

 terior valve small, slightly emarginate behind ; mucro terminal, slightly 

 raised, from the elevated postero-lateral ribs the fine stria- diverge 

 straight in front, obliquely on the posterior area. Girdle has, viewed 

 with an ordinary pocket-lens, the appearance of being minutely scaly, 

 but a more powerful lens reveals the fact that the whole surface is 

 densely pitted ; near some of the sutures tufts of a few light-coloured 

 bristles, and a few hairlets near the margin ; it seems probable that the 

 bristles are deciduous. Colour blackish-green, girdle a little darker ; 

 the anterior valve with a few concentric light-blue zigzag bands ; 

 the intermediate valves have a number of wavy longitudinal blue 

 streaks running over the lateral and central tracts ; the posterior- 

 valve with an indistinct blue patch on each side ; anterior valve 

 with 8 slits ; teeth strong, broadly grooved on the outside ; inter- 

 mediate valves with 1 slit on each side ; posterior valve with a smooth 

 insertion plate and a posterior median sinus. 



Length, 17 mm. ; breadth, 13 mm. Divergence, 108. 



Type in my collection. 



Hab. Near entrance to Kawhia Harbour, on rocks at half-tide, 

 much exposed to heavy seas, type (R. Murdoch) ; Port Molyneux 

 (Dr. Torr). 



Remark. Sculpture similar to that of biramosa and ccplata^ but 

 much finer. 



6. Plaxiphora superba, Pilsbry, 1893. Plate 2, fig. 6 ; Plate 3, fig. 14. 



Plaxiphora superba, Pilsbry, Man. Conch. (1), xiv, 319, pi. 68, f. 55-61. 

 P. subatrata, Suter, P. Mai. S-, ii, 1897, 190, f. 7-11. 



Shell large, oval, moderately elevated, dorsal ridge acute, rounded 

 and worn off in old specimens, reddish-olive, brown, or olive, with a 

 few transverse blackish bands, girdle with sutural pores. Anterior 

 valve subangled by 8 radii, which slightly undulate the peripheral 

 margin ; otherwise nearly smooth except for growth-lines, or strongly 

 concentrically ridged and the ribs almost obsolete. Intermediate 

 valves nearly rectangular, transversely elongate to very narrow, having 

 a " false apex " in front, and more or less distinctly beaked behind ; 

 the whole surface smooth except for growth-lines, and 2 flat, sometimes 

 nodulous, ribs bounding the but-little-raised lateral areas ; the ribs 

 may increase to 4. Posterior valve small, depressed, concentrically 

 ridged, mucro subposterior to terminal, but little elevated. Girdle. 



