CONCHOLOGY. 47 



equilateral ; the cardinal and the lateral teeth well marked ; 

 the muscular impression anterior, rounded. 



7. Lucina. Twenty species. 

 In the hinge and lateral teeth it much resembles the Tel- 

 lina, but differs from it in never being flexuous. This genus 

 is more easily characterized by the orbicular, compressed, 

 general form of the shell, than by the dental system, which 

 is sometimes entirely effaced. 



Shell compressed, regular, orbicular, sub-equilateral ; sum- 

 mits small and pointed, inclined anteriorly ; hinge similar, 

 but variable ; two divergent cardinal teeth, little marked, and 

 sometimes entirely effaced ; two remote lateral teeth, with a 

 pit at the base, sometimes obsolete ; posterior ligament more 

 or less sunk ; two widely-separated muscular impressions, 

 of which the anterior is narrow and long. 



Lucina Jamaicensis. Lucina concentrica. 



L. Pennsylvanica. L. divaricata. 



L. edentula. L. carnaria. 



L. mutabilis. L. scabra. 



L. radula. L. reticulata. 



L. squamosa. L. sinuata. 



L. lactea. L. pecten. 



L. undata. L. lutea. 



L. circinaria. L. digitalis. 



L. columbella. L. globularis. 



L. Jamaicensis. The Jamaica Lucina. PI. 8, fig. 8. 

 Species lenticular, striated concentrically ; the teeth of the 

 hinge variable, and sometimes obsolete. 



L. undata. The waved Lucina. 



Orbicular, thin, convex, undulated with fine irregular striae; 

 exterior pale yellow, interior white ; margin glossy and plain. 



8. Donax. The Wedge Shell. Twenty-seven species. 



The singularity of form that gave rise to its common 

 name renders it easily distinguished. It very much resem- 



