Maryland Gkological Survey 375 



Virginia ; Warren Point, Pennsylvania. BECRiVFT Member. Cherry Eun, 

 West Virginia. Oriskany Formation, >Siiriver Member. North 

 Branch. Ridgely Member. Knobly Mountain near Cumberland, 21st 

 Bridge. 



Collections. — Maryland Geological Survey, American Museum Natural 

 History (figured forms). 



Eatonia sinuata Hall 

 Plate LXV, Figs. ;iG-38; Plate LXVI, Fig. 1 



Eatonia sinuata Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., 



p. 91. 

 Eatonia sinuata Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 438, pi. cia, figs. 



3-6. 

 Eatonia sinuata Hall and Clarke, 1893, ibidem, vol. viii, pt. ii, p. 206, pi. Ixi, 

 figs. 36-38. 



Description. — " Shell circular or longitudinally oval : ventral valve 

 concave, except in the umbonal region, from which point, as well as from 

 the lateral margins, it slopes generally into the broad deep sinus without 

 deliiied margins: dorsal valve convex, rising in front into a broad unde- 

 fined mesial prominence, often nearly as high as the highest part of the 

 central region of the valve; beak incurved. Surface marked by thirty-six 

 to forty [the illustrations show a variation between 26-34] strong, elevated, 

 rounded or subangular plications on each valve. A^isceral impressions 

 large, broad, and marked with radiating plications towards the margin, 

 strongly defined by an elevated border : impression of the adductor muscles 

 cardiform, small, located in the middle of the visceral impi'ession, longi- 

 tudinally striate. 



" The two middle plications on' the dorsal valve are separated by a wider 

 depression than between those on other parts of the shell, which continues 

 quite up to the beak: in this depression there is sometimes near the front 

 a slender plication which becomes obsolete before reaching the beak.'' 

 Hall, 1857. 



Some excellent material of this fine and large brachiopod has been 

 found during the past few years. This shows that all the plications on 

 each side of the undefined fold and sinus are covered with fine radial 



