MARYLAND GEOLOGICAL SURVEY 391 



In Say's description above the two ends have been transposed, so that 

 for anterior, posterior, before, behind, etc., read the opposite term. The 

 ■very anterior position of the beak, the longer line of finer, narrower teeth 

 and smaller size of the shell distinguish it from A. limula. 



Length, 40 mm. ; height, 22 mm. ; diameter, 11 mm. 



Occurrence. — Choptank Formation. Jones Wharf, Dover Bridge 

 (rare and small). 



Collection. — U. S. National Mnsenm. 



Subgenus BARBATIA (Gray) Adams. 

 Section STRIARCA Conrad. 



Arca (Baebatia) centenaeia Say. 

 Plate CVI, Figs. 5, 6. 



Area centenaria Say, 1824, Jour. Acad. Nat. Sci. Phila., voL iv, 1st ser., p. 138, 



pL X, fig. 2. 

 Arca centenaria Conrad, 1832, Fossil Shells of the Tertiary, p. 16, pi. i, tig. 4. 

 Arca centenaria Conrad, 1840, Fossils of the Medial Tertiary, p. 55, pi. xxix, tig. 4. 

 Arca centenaria Tuomey and Holmes, 1856, Pleiocene Fossils of South Carolina, 



p. 37, pi. xiv, figs. 11, 12. 

 Arca centenaria Emmons, 1858, Rept. N. Car. Geol. Survey, p. 285, fig. 205. 

 Striarca centenaria Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 580. 

 Striarca centenaria Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 6. 

 Arca (Striarca) centenaria Whittield, 1894, Mon. xxiv, U. S. Geol. Survey, p. 42, 



pi. vi, figs. 5-7. 

 Barhatia (Striarca) centenaria Dall, 1898, Trans. Wagner Free Inst. Sci., vol. ill, 



pt. iv, p. 628. 



Description. — " Shell transversely-oval, subrhomboidal, obtusely con- 

 tracted at base, with numerous alternate longitudinal striae. 



" Striae from one hundred to one hundred and eighty and more in 

 number; disappearing on the hinge margin; with hardly obvious trans- 

 verse minute wrinkles, and larger,. remote, irregular ones of increment; 

 beaks but little prominent, not remote; base widely but not deeply con- 

 tracted, nearly parallel with the hinge margin; anterior and posterior 

 margins obtusely rounded; series of teeth rectilinear, uninterrupted, de- 

 curved at the tips ; space between the beaks with numerous grooves pro- 

 ceeding from the teeth ; inner margin not very distinctly crenated ; mus- 

 cular impressions elevated, and forming a broad line each side, from the 

 cavity of the beak to the margin." Say, 1824. 



