SUTER : REVISION OF THE NEW ZEALAND POLYPLACOPHORA. 67 



Plaxiphora (s. str.) murdoehi, n, sp. 



PI. ix, fig. II. 



Shell rather small, oval, slightly narrowed behind, roundly angled along 

 the top of the valves, blackish-green, finely sculptured, intermediate valves 

 mucronated, girdle rather narrow, of a minutely scaly appearance and 

 with sparse hairlets. Anterior valve radiately eight ribbed, with five diverging 

 striae, which are coarser near the anterior margin, and from elongated 

 nodules on the posterior edges. Intermediate valves with a lighter coloured 

 posterior mucro, the whole surface scul[)tured with fine striae ; the lateral 

 areas are distinctly marked off by an elevated ridge descending from the 

 jugum and dissolving into numerous fine striae near the margins, the stride 

 on the lateral areas and the pleural tracts are arranged in such a way that 

 they radiate from the ridge like the webs from the shaft of a feather. The 

 posterior margin has a row of nodules on eaeh side, like the anterior valve. 

 Central area with diverging riblets in front of the mucro, but straight and 

 parallel to the jugum on the remaining surface. Posterior valve smnll, very 

 slightly emarginate behind ; mucro terminal, slightly raised, from the 

 elevated postero-lateral ribs the fine riblets diverge straight in front, obliquely 

 on the posterior side. 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 girdle is densely and regularly pitted. Near some of the 

 sutures I found tufts of a few light coloured bristles, and a few hairlets were 

 found near the margin of the girdle, but it was not easy to find them. It 

 seems most likely that the whole girdle was originally densely covered with 

 fine, short hairlets and tufts near all the sutures, but that they are very easily 

 rubbed off Colour blackish-green, girdle a little darker. The anterior valve 

 has a fevv concentric zigzag bands of light blue ; the intermediate valves 

 have a number of wavy, longitudinal blue streaks, running over the lateral 

 and pleural tracts ; the posterior valve has only an indistinct blue patch on 

 each side. Interior blue, the sutural laminte white. Sinus rather narrow, 

 straight, the'sutural laminae broadly arched, short. Anterior valve with 8 

 slits, corresponding to the external ribs, teeth strong, liroadly grooved on the 

 outside ; intermediate valves with i slit on each side, corresponding with 

 the ril)s of the lateral areas ; posterior valve with a smooth insertion plate 

 with a posterior median sinus, no slits. 



Length 17, breadth 13 millim. ; divergence 108°. 



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

 Much exposed to very heavy seas. (R. Murdoch). 



Type in my ccjllection. 



With regard to the sculpture this species stands nearest to P. Uramosa 

 and c.apJafa, but in l.oih of these it is much coarser. The beautiful fine 

 sculpture, colour, an. I the curiously pitied girdle, when devoid of h.u'rs, 

 separate it at once from the two. 



