280 POLYPLACOPHOKA OF LORD HOWE AND NORFOLK LSr.ANDS, 



found by Mr. T. Tredale on Raoiil or Sunday Island, Kermadec 

 Group.* 



Onithochiton discrepans, n.sp. 



(Plate xiii., figs. 9, 9«, 9h, 9f, M, 9.-, 9/.) 



►Shell elevated, the dorsal ridge rounded. Colour olive-buff", 

 variabl}- llamed with orange, wood-brown, and green. The colour 

 of different specimens varies considerably; in some the orange 

 predominates, others are chiefly green. 



Anterior valve ha^•ing 8 or 9 radiating ribs, distinctly raised, 

 and concentricallj' grooved, separating 9 or 10 rows of ocelli; the 

 posterior margin of the valve with smooth thickened ridge. 



Posterior valve smooth, mucro posterioi'. 



Median valves moderately l)eaked, the lateral areas raised, 

 radially grooved by 4 to 6 furrows; rows of ocelli between the 

 anterior rib and the furrows. Central areas with shallow sulci 

 originating at and denticulating tlie anterior rib and vanishing 

 towards the margin. 



Girdle leathery, two-thirds the width of exposed portion of 

 valves, pale yellow, veined with orange-brown: densely clothed 

 with microscopic down. 



Interior pearly-white; sinus broad, deep, denticulate. Anterioi' 

 valve having 8 and median valves I-l slits. 



Length 19 mm., breadth ll'mra. 



Station. — In interstices of waterworn fragments of coral rock, 

 or attached to the rocky sides of pools in the reef at low tide. 



Habitat. — Lord Howe Island. 



Ilemarks. — This shell is not plentiful. Its habit of occupying 

 holes in stones somewhat resembles that of Cryptoplax. Com- 

 pared with the Australian 0. qiterciims, the new species is 

 apparently far smaller. In the median valves of 0. diHcrejiatis 

 the eye-rows part radial from transverse ridges, whereas uninter- 

 rupted transverse ridges prevail in 0. (/uercinus. The anterior 

 valve of the Australian form is concentrically furrowed, but in 

 the T..ord Howe Island species radial ridges are dominant. 



• Iredale, Proc. Malao. Soc. ix., 1910, p. 161. 



