BY CHARLES HEDLEY AND ARTHUR WILLEY. 109 



buttress of callus. A deep sinus is formed by the projection of 

 a tongue of non-naci'eous shell, as shewn in the figures accompany- 

 ing this paper. 



Operculum. — Slightly hollowed out on its external surface, very 

 sharply angled on the distal margin, thick and regularly oval. 



Dimensions of adult shell. — Height 26 mm., major diameter 

 45 mm. (maximum measurement), minor diameter about 39 mm. 



EXPLANATION OF PLATE. 



In both figures the Vmttress of callus is sViovvii at the upper angle of the 

 aperture. In Fig. 2 only a portion of the bead-rows have been inserted; 

 this specimen had four rows about the central callus, and a row of very 

 small beads at the bottom of the subm<rginal furrow (indicated by the 

 dark shading). Finally, in Fig. 2, the non-nacreous tongue at the outer 

 margin of the aperture, mentioned in the text, is indicated by the dotted 

 line dividing it off from the nacreous portion of aperture. 



