- 101 - 



Description ,- "Shell rather thin, brown or ''ororTiish purple, 

 adherinf f^o msjio-rovf's y>-^' elongated lobes '^-^ "?->'^ irr'(^-r v.oiye. up_ 

 per yslve in the middle elevate'"! into a tiihe-shajpec rib, all the 

 sides divergently? ribbel; ribs, roimded, smooth," (Reeve, 1071). 



The 'Sow den -"-"- referred to this species are sniall and thin- 

 shelled; otitline variable, long-itudinallj? subovate to elongate 

 and narrow; left valve usually more convex than the right; longi- 

 tudinally swollen medially; mar^-^lns of the valvep ^r,,.i:^-'-,.-r^r^r -^-i-f-v 

 fifteen to twenty sharp, usually sub-rounde^l plications oeooming 

 smaller dorsally and e2:tendin!? only a short distance from the margin, 

 the central portion of the shell almost smooth or bearing cnrved 

 clasping spines; concentric sciilpture of inconspicuous incremental 

 lines; lip-ament area small, flattened; muscle scars small, subellip- 

 tical to subcircxilai iix outline, usually posterior in position; 

 inner margin of the shell, or onlj portions of the mare-in, often 

 bearing small pustules. 



Dimensions .- Tat. 1] mm. ; alt. , 34 mm, 



Remarks . - i'hese forms are the most puzzling of this unsatis- 

 factory assemblage of oysters. They cannot be separated from the 

 recent ''/est Indian group which has been reported under varioiis 

 names,- C. folium Linnaeus, 0. cristata Born and 0. narasitica 

 Jmelin, Since this soecies has n^t been recorded in the Tertiary 



