646 CRETACEOUS PALEONTOLOGY. 



Family SAXICAVIDAB. 



Genus PANOPEA Menard. 



Panopea decisa Conrad. 



Plate LXXIII, Figs. 3-5. 



1853. Panopaa decisa Con., Jour. Acad. Nat. Sci. Phil., 2nd 



ser., vol. 2, p. 275, pi. 24, fig". 19. 

 1861. Glycimeris decisa Gabb, Synop. Moll. Cret. Form., p. 



181 (125). 

 1864. Panopaa decisa Meek, Check List Inv. Foss. N. A., Cret. 



and Jur., p. 15. 



1868. Glycimeris decisa Con., Cook's Geol. N. J., p. 727. 

 1868. Panjopea decisa Whitf., Pal. N. J., vol. i (Monog. U. S. 



G. S., vol. 9), p. 181, pi. 24, figs. 5-8. 

 1905. Panopea decisa Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 18. 



Description. The dimensions of a large specimen are : length, 

 about 80 mm.; height, 51 mm.; thickness, 35 mm. Shell more 

 or less subelliptical in outline, widely gaping behind and closed in 

 front. Beaks central or a little in front of the center of the shell, 

 moderately large and incurved. Hinge-line nearly straight; an- 

 terior margin rounded, its greatest extension below the middle; 

 basal margin nearly straight or gently convex; usually subpar- 

 allel with the hinge-line; posterior margin curving more or 

 less abruptly upward and backward from the basal margin, 

 obliquely truncate below, rounding into the cardinal margin 

 above. Valves rather ventricose, with a rounded, oblique, an- 

 terior, umbonal ridge becoming broader and more or less obso- 

 lete below ; from the umbo the surface slopes rather abruptly in 

 front and gently behind; from the posterior side of the beak a 

 rather broad, shallow, indefinite sinus extends obliquely back- 

 wards towards the postero-basal angle, usually becoming obsolete 

 in the outer portion of large individuals. Surface of the shell 

 marked by strong, more or less irregular, concentric undulations. 



