CRETACEOUS FOSSILS. 217 



PLACUNANOMIA, Brod. 



P. LNORNATA, U. 8. 

 PI. 32, Fig. 28$, and 288 a. 



SHELL thin, irregular, inequivalve ; upper valve convex, usually 

 narrowest near the beaks, broad towards the base ; hinge-margin 

 thickened ; surface marked by fine radiating lines, or smooth, 

 usually concentrically undulated ; lower valve concave, without 

 the radiating lines; hinge-line but little, if at all, thickened; 

 foramen small, bordered on one side by a thickened margin. 



Figures, natural size. 



Localities: Near San Diego, Mr. Morse; and north of Corral Hollow. Abun 

 dant at both localities. 



PAL. VOL. I. 28 



