178 SYSTEMATIC PALEOXTOLOGT 



land, no reference is made to it in the synonymy. If the figure and 

 description are correct, it is probably a different species from any in 

 Maryland. 



Yexeeicaedia plaxicosta yae. eegia Conrad. 



Plate XXXVIII, Figs. 1, la; Plate XXXIX, Figs. 1, la; 

 Plate XL, Figs. 1, 2, 3. 



CarcUta planicosta Conrad, 1832, Fossil Shells of the Tertiary, No. 1, [1st. edit.} 



p. -30, pi. V, fig. 2. 

 Cardita planicosta Morton, 1834, Syn. Org. Rem. Cretaceous Group, App., p. 7. 

 Venericardia planicoata H. C. Lea, 1848, Proc. Acad. Nat. Sei. Phila., vol. iv, p. 107. 

 Venericardia planicosta var. regia Conrad, 186.5, Amer. Jour. Conch., vol. i, p. 8. 

 Venericardia planicosta Conrad, 1866, Smith. Misc. Coll. (200), p. 5. 

 Vetiericardia regia Conrad, 1866, Smith. Misc. Coll. (200), p. 5. 

 Cardita planicosta Heilprin, 1884, Contrib. Tert. Geol. and Pal., p. 87. 

 Venericardia planicosta var. regia Harris, Amer. Jour. Sci., ser. iii, vol. slvii, 



p. 302. 

 Venericardia planicosta Clark, 189.5, Johns Hopkins Univ. Circ, vol. xv, p. 5. 

 Venericardia planicosta Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 80, pi. xxi, 

 fig. 3 ; pi. xxii, fig. 2; pi. xxiii, figs. \a (?) 1& (?) Ic; pi. xxiv, figs, la (?) 16 (?) 

 Ic; pi. XXV, figs, la-lc. 



Description. — The form originally described and figured by Conrad, 

 "«'hich he subsequently called Y. regia, seems to correspond very closely 

 to the original Y. planicosta of Europe. Conrad describes it as follows: 



" Cordate; ribs about 22, broad and flattened, separated by a narrow 

 grooTB which becomes obsolete at the base; ribs near the posterior end 

 narrow, indistinct, and crossed by numerous strong wrinkles; lunule 

 small; cordate, profoundly impressed; inner margin crenate." Conrad, 

 1832. 



This form is the largest of our Eocene Yenericardias and is widely 

 distributed in and restricted to the Aquia formation. It. is readily dis- 

 tinguished by its size, and its broad, flat ribs, which do not become obso- 

 lete. 



Length, 110 mm.; width, 100 mm. 



Occurrence. — Aquia Foemation. Upper Marlboro, 1 mile west of 

 Hardesty, Sheckels Farm near South Eiver, 1 mile northeast of Piscat- 

 away, Near Annapolis, Aquia Creek, Potomac Creek, CoUington, 

 Eolphs Landing, Mouth of Paspotansa Creek, Fredericktown (Cecil 



