Maryland Geological Survey 373 



bifurcating strias; a stronger elevated one along the center of the mesial 

 sinus, and a narrow longitudinal depression down the center of the dorsal 

 valve, the mesial elevation of which is sometimes obtusely subplicate near 

 the margin." Hall, 1859. 



Length about 17 mm. ; width 15 mm. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Miller's Spring near Cumberland, 21st Bridge, Maryland; Cherry Kun, 

 West Virginia. Becraft Member. North Mountain, Maryland ; Warren 

 Point, Pennsylvaniii. Oriskany Formation, Eidgely Member. Cum- 

 berland (Knobly), Colliei-'s Eun, Hancock, Maryland; Keyser, West, 

 Virginia. 



Collection. — Maryland Geological Survey. 



EatONIA WIIITFIELDI Hall 



Plate LXV, Figs. 29, 30 



Eatonia whitfleldi Hall, 1859, Nat. Hist. N. Y., Pal., vol. ill, p. 437, pi. cia, 

 figs. 2a, 26, 1861. 



Description. — " Shell longitudinally suboval, wider below than above. 

 Ventral valve depressed convex near the beak, fiat in the middle, and 

 broadly depressed towards the front. Surface radiatingly plicated : plica- 

 tions rounded, about eight or nine on each side of the mesial one, which is 

 a little stronger than the others. Muscular impression of the ventral valve 

 broad, and not strongly defined : crural processes short." Hall, 1859. 



Length 19 mm. ; width 22 mm. 



When the sinus is deeply impressed there is usually but one plication in 

 it, as described by Hall, but when broad and undefined there are always 

 three. On the lateral portion of the valve there are usually six to seven 

 plications. The small size and few plications Avill readily distinguish this 

 species from the other plicate Eatonias. The Maryland specimens, how- 

 ever, are always more acuminate than New York individuals, and the 

 plications are better defined. 



Occurrence. — Oriskany Formation, Eidgely Member. Knobly 

 Mountain near Cumberland. 



Collections. — U. S. National Museum, George M. Eoeder (figured 

 forms). 



