192 SYSTEMATIC PALEONTOLOGY 



and Florida. It ranges in the Eecent from Massachusetts Bay southward 

 to Florida and along the coast of the Gulf of Mexico to Yera Cruz, 

 Mexico. 



Length, 30 mm.; width, 33 mm. 



Occurrence. — Talbot Formation. Wailes Bluff near Cornfield Har- 

 bor, and Langleys Bluff, St. Mary's County. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 and U. S. National Museum. 



Class PELECYPODA. 



order TELEODESMACEA. 



Superfamily ADESMACEA. 



Family PHOLADIDAE. 



Subfamily PHOLADINAE. 



Genus BARNEA (Leach ms) Risso. 

 Subgenus SCOB1NA Bayle. 



Baenea (Scobina) costata (Linne) 



Plate LII. 



Pholas costatus Linne, 1758, Syst. Nat. ed. x, p. 669. 



Pholas costata Holmes, 1858, Post-PL Fos. S. C, p. 58, pi. ix, fig. 1, la. 



Pholas (Barnea) costata Dall, 1889, Bull. U. S. Nat. Mus., No. 37, p. 72, pi. 



lxviii, fig. 9. 

 Barnea (Scobina) costata Dall, 1898, Trans. Wagner Free Inst. ScL, vol. iii, 



pt. iv, p. 816. 



Description. — " Ph. testa ovata costis elevatis striata." Linne, 1758. 



This delicate and fragile form is larger and thinner than the Miocene 

 B. arcuata which is probably its ancestor and with which it has many 

 characters in common. It has a shorter umbonal reflection, while the 

 thin valves result in a characteristic punctate pattern on the interior. 

 The earliest appearance of B. costata is in the Pliocene of North Caro- 

 lina and Florida. In the Pleistocene it occurs in Massachusetts, Mary- 



