PLAXIPHOEA. 323 



Group of P. petholata. 



Shell somewhat sculptured. Girdle covered with crisp hairs, not 

 forming bunches at the sutures, nor having pores there. 



P. PETHOLATA Sowerby. PI. 68, figs. 62, 63, 64, 65, 66, 67. 



Shell elliptical or oblong, rather depressed, the dorsal angle 

 rounded but side-slopes rather straight. Surface finely corrugated at 

 the sides, nearly smooth in the middle. Color black or blue-black, 

 with pink, creamy or greenish-white angular markings at the sides, 

 and a wide triangle of the same light tint on the ridge of each valve, 

 generally enclosing a dark, ill-defined dorsal stripe. 



The median valves are slightly beaked. Lateral areas hardly 

 raised, defined by a narrow, inconspicuous and slightly curved 

 diagonal riblet, the surface finely corrugated in zig-zag or vermic- 

 ulate pattern. Central areas corrugated zigzagly at the sides, in front 

 of the diagonal rib, the corrugation becoming finer toward the middle, 

 and giving place to a microscopic pattern resembling a dense punctula- 

 tion united with a minute zigzag or vermiculate wrinkling. Anterior 

 valve having about 9 narrow radiating riblets, the intervals densely 

 and finely zigzag-punctate. Posterior valve depressed, wide and 

 short, the mucro at the posterior edge, slightly acute and a little 

 elevated ; posterior area of the valve very narrow, ill-defined. 



Interior dark blue-green. Sinus deep, wide, angular, its edge light 

 brown and very spongy. Anterior valve having 8 slits, correspond- 

 ing to external riblets, central valves 1 slit ; the teeth acute, some- 

 what thickened at the edges of the slits. Posterior valve having a 

 rather blunt, smooth insertion plate, interrupted by a shallow sinus 

 in the middle behind. Eaves very narrow, spongy. 



Girdle rather wide, black-brown and brown alternately, rather 

 densely clothed with corneous or dark brown bristles, large and 

 small, not in the least arranged in series or issuing from sutural 

 pores. 



Length 40, breadth 27 mill. ; divergence 125. 



Length 32, breadth 18 mill. ; divergence 130. 



Length 45, breadth 25 mill. 



Australia (Sowb.) ; Tasmania (Cuming.) 



Chiton petholatus SOWB., Mag. of Nat. Hist. New Series, iv, p. 

 289 (May, 1840) ; Conchol. Illustr., f. 64, 65, and var. porphyrius, 

 f. 59. REEVE, Conch. Icon., f. 74. Euplaciphora petholata CPU., 

 MS. Not Plaxiphor a petholata ANGAS, P. Z. S. 1865, p. 187 and 



