Maryland Geological Survey 315 



regular concentric wrinkles which curve outwards on approaching the 

 hinge. Interior of shells striato-punctate, the hinge-line crenulated 

 almost to its extremities. The muscular area of the ventral valve flabelli- 

 form, more or less strongly defined at its margins." Hall, 1859. 



Length 4 cm. ; width 4.5 cm. 



Mr. Roeder collected a single small specimen on Knobly Mountain in 

 the Upper Oriskany, which may belong to this species. It has fewer con- 

 centric corrugations, and these are restricted to an area in the posterior 

 region smaller than in the Helderberg specimens, and there are fewer un- 

 dulating striae. In Helderberg individuals there are about seventeen of 

 these in 10 mm., while in that from the Oriskany there are fifteen in the 

 same space. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Cedar Cliff, West Virginia; 21st Bridge, Maryland ; Warren Point, Penn- 

 sylvania. Oriskany Formation, Eidgely Member. Knobly Mountain, 

 near Cumberland. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



StROPHEODONTA (LEPTOSTROnilA) PLANULATA (Hall) 



Plate LVII, Figs. 14-lG 



Strophodonta planulata Hall, 1S59, Nat. Hist. N. Y., Pal., vol. iii, p. 184, pi. 

 xvi, figs. 9-12, 1861. 



Description. — " Shell semielliptical, width nearly one-half the length, 

 plano-convex: hinge-line greater than the width of the shell below; the 

 cardinal extremities often salient. Dorsal valve flat. Ventral valve uni- 

 formly and very slightly convex, sometimes flattened towards the margins : 

 beak scarcely elevated above the hinge-line. Area linear. Foramen un- 

 known. Surface finely and evenly striated : striae of the dorsal valve often 

 flattened. Eadiating striae crossed by fine closely arranged concentric 

 strife, and sometimes with a few inconspicuous laminaj of growth, and 

 towards the cardinal extremities by a few wrinkles or undulations." Hall, 

 1859. 



Length about 3 cm. : width about 4 cm. 



