PLAXIPHORA. 321 



with large sutures. Entire surface smooth, generally eroded, sub- 

 spongy. Interior; posterior valve with a moderately elevated 

 insertion-plate, moderately sinuated behind. Anterior valve with 8, 

 median valves 1 slit ; teeth acute, scarcely thickened at the edges of 

 the slits. Eaves short, spongy. Sinus very narrow, smooth, straight. 

 Girdle spongy, having very close, small hairlets, and longer corneous 

 hairs scattered and at the sutures. (Qpr.) 



Length 1*35, breadth *7 inch, divergence 120. 



Var. : length I'l, breadth '65 inch, divergence 100. 



Tristan Island, Tristan da Cunha, on the shore, and off Nighten- 

 gale Island, Tristan da Cunha, 100-150 fms. ('Challenger.') 



Euplaciphora simplex CPU., MS. Plaxiphora simplex CPU., in 

 Haddon's Keport on the Polyplacophora of the Challenger Expedi- 

 tion, p. 33. Also described by HADDON, 1. c., p. 34, t. 3, f. 13, 

 13a-c. 



This species I have not seen. The P. modesta alluded to by Car- 

 .penter is a form of P. petholata. 



Haddon describes P. simplex as follows : 



Shell smooth, simply marked with line of growth, flat sides meet- 

 ing at a variable angle. Anterior valve small, surface smooth. 

 Under surface with eight slits, teeth fairly long, smooth and sharp ; 

 eaves short. Intermediate valve : Central area ; smooth, flat. 

 Lateral areas inconspicuous, with two or three very faint radiating 

 ridges. Under surface with a median horizontal rib-like swelling ; 

 sutural laminse broad, but not deep ; jugal sinus wide and shallow ; 

 one lateral slit ; eaves short. Posterior valve very small and flat, 

 greatly corroded; umbo apparently flat and terminal; posterior 

 border thickened. Under surface : sutural laminae as in intermediate 

 valves, but the jugal sinus is comparatively narrow and deep; slits 

 and teeth absent ; posterior border much swollen. 



Girdle very thick and fleshy, upper surface having a spongy 

 appearance, owing to being beset with very short horny spines, 

 which are scarcely raised above the surface ; there are tufts of longer 

 spines, three to nine in each tuft, opposite the sutures of the valves; 

 these have no definite position round the anterior valve. Situated 

 outside these are numerous scattered similar tufts, usually somewhat 

 smaller in size, which pass into an imperfect peripheral fringe of 

 spines, (pi. 67, figs. 44, 46). Color : all the valves of a uniform 

 dark brown, with a pale (lilac) narrow triangular band along the 



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