SHELLS. 453 



PLATE XLII. Figs. 5, 6. 



ABGA (BYSSOAEGA) DUBIA, Baircl. 



Shell ovately oblong ; posterior extremity rather acute ; an- 

 terior rather squarely rounded ; keel well marked, running down 

 from beaks to end of posterior extremity ; of a dull white colour 

 without any markings ; longitudinally ribbed, ribs small till they 

 reach the keel, crossed with strong transverse raised ridges which 

 are almost beaded ; posterior concave and divaricately rayed with 

 4 or 5 strong ribs ; umbones situated near anterior extremity ; 

 ligamental area very small and narrow, colourless ; ventral margin 

 slightly sinuated. 



Length nearly i an inch. 

 Greatest breadth 3 lines. 

 Hab. New Caledonia. 



Approaches A. divaricata of Sowerby from west coast of 

 America ; but the shell is narrower, the anterior extremity less 

 rounded, the hinge area more narrow ; and the body of the shell 

 is not fimbriately ribbed. 



PLATE XLIL Fig. 7. 

 PEGTEN SIMILIS, Baircl. 



Shell somewhat orbicularly ovate, a little longer than broad, 

 equilateral, equivalve ; valves rayed with 25 ribs ; ribs rather 

 narrow, squamate : scales very minute at upper part, larger on 

 ower portion and at the sides, standing almost erect, thin, and 

 rather broad. Shell externally of a dull reddish colour, internally 

 of a pale red and somewhat iridescent ; ears unequal, ribbed and 



