Plaxiphora.} AMPHINEURA. 23 



Remarks. The validity of this section seems to me rather doubt- 

 ful, as the encroachment of the girdle is an extremely variable cha- 

 racter. The only species known is the type. Dried specimens very 

 often show no encroachment of the girdle at all. 



7. Plaxiphora obtecta, Pilsbry, 1893. Plate 2, fig. 7. 



Plaxiphora obtecta, Pilsbry, Man. Conch. (1), xiv, 330. Mopalia ciliatcu 

 Sowerby: Hutton, M.N.Z.M., 11(3, not of Sowerby. Plaxiphora Suteri. 

 Pilsbry," "Nautilus," viii, 1894, 8 : Suter, P. Mai. S.. ii, 190. P. glauca. 

 Q. & G. : Wissel, Zool. Jahrb., Syst,. xx, 606, pi. 21, f. 19 ; pi. 22, f. 20, 21 

 (anatomy); not of Quoy and Gaimard. 



Shell large, oval, olive-brown, nearly smooth, broad, partly covered. 

 Anterior valve smooth, with very fine growth-lines, but rarely with 

 subobsolete radial ribs. Intermediate valves smooth, distinct growth- 

 lines near the anterior margin ; lateral areas indistinct, but. there is a 

 slight indication of a diagonal rib. Posterior valve transversely finely 

 striated, mucro terminal, low. Girdle broad, narrower at the ends, 

 sometimes encroaching at the sutures to a considerable extent, the 

 girdle reaching to within a short distance of the jugal tract ; there 

 are no sutural pores, but amongst the bristles scattered more or less 

 densely there are a number of tufts with 2 to 3 larger bristles, and of 

 these 1 may occasionally be situated near a suture. Colour as a rule 

 olive-brown, a white ridge running down the centre, wedge-shaped 

 on each valve, and with a central reddish-brown stripe ; head valve 

 with small blue dots, sometimes with blue zigzag bands ; the other 

 valves with blue zigzag markings of various size ; more often the 

 whole surface is yellowish-brown, lighter upon the dorsal ridge. In- 

 terior blue, fading to white on the sutural plates ; anteiior valve 

 with 8-9 slits, teeth strong, sharp, finely striated on the outside ; 

 intermediate valves with 1 slit on each side, posterior tooth pointed ; 

 end valve with a broad, low, rounded insertion plate ; on valves 

 1-7 the tegmentum is overreaching the articulamentum on the pos- 

 terior margin ; the sinus is broad, slightly spongy ; sutural lamina? 

 strong, high, rounded ; valve-callus stout. 



Length, 50 mm. ; breadth. 32 mm. : divergence, 120 (type). 

 Length, 48 mm. ; breadth, 27 mm. (medium-sized specimen). Length, 

 87 mm. ; breadth, 57 mm. (my largest specimen). 

 Type in the British Museum. 



Hab. Coasts of both Islands, more common on the west coasts ; 

 on rocks exposed to the full force of the surf. The very large speci- 

 men was collected by Captain Bollons on Canoe Rock, in the Hauraki 

 Gulf. 



Remarks. The species was described by Carpenter in MS., and 

 published by Pilsbry. 



P. Suteri, Pils., is founded on a dry specimen showing almost no 

 encroachment of the girdle. Carpenter says that the girdle is sinuated 



