p.3

Corbis undata, Conrad, Tert. Foss. p. 40. Am. Jour. Sc. 2d. Ser. vol. 1 p. 401 pl. 4 fig. 11.-C. distans Con. Tert. Foss. p. 40 [immature shell].

Ovate ventricose, with about twelve concentric ribs or undulations, very strongly prominent, acute, remote on the umbo, lamelliform towards the apex, but thick, less prominent and approximate towards the middle of the valve; on the inferior half of the valve are irregular concentric impressed lines; disk with radiating lines; obsolete on the middle of the inferior half of the valve, profound on the sides, crenulated on the anterior sides; posterior side with distant [prominent] prominent lamellae five or six in number; beaks medial;