Maryland Geological Survey 341 



dorsal valve unknown ; hinge-line equal to the greatest width of tlie shell, 

 terminating in minute triangular extensions; area sublinear, incurved 

 beyond the plane of the valves. Surface unknown." Hall, 1857. 



Length 10-12 mm. ; width 14-20 mm. 



Occurrence. — Oriskany Formation, Shriver Member. Devil's Back- 

 bone, Winchester Eoad near Cumberland, North Branch, 21st Bridge. 

 Eidgely Member. Williams Eoad near Cumberland. 



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



Genus CHONOSTROPHIA Hall and Clarke 



Chonostrophia complanata (Hall) 

 Plate LXII, Figs. 1, 2 



Chonetes complanata Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., 



p. 56. 

 Chonetes complanata Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 418, pi. xcili, 



fig. 1, 1861. 

 Chonostrophia complanata Hall and Clarke, 1892, ibidem, vol. viii, pt. i, p. 



311, pi. xvi, figs. 13, 29. 

 Chonostrophia complanata Clarke, 1900, Mem. N. Y. State Mus., vol. iii. No. 3, 



p. 50, pi. vii, figs. 1-13. 

 Chonostrophia complanata Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. 



348, pi. xlvi, fig. 12. 



Description. — "Shell nearly semicircular, compressed? about two- 

 thirds as long as wide: ventral valve flat or concave: dorsal valve un- 

 known ; tubular spines of the cardinal margin directed obliquely outwards. 

 Surface marked by fine, closely arranged (bifurcating?) striifi, which 

 appear to have been crenulated by closely arranged concentric stri;iL>. Some 

 of the specimens show distant imbricating concentric lines of growth : 

 interior finely granulose ; viscera impression large, uniform, not strongly 

 marked." Hall. 1857. 



Length about 1.7 cm. ; width about 2.8 cm. 



While this species has great geographic distribution, it seems never to 

 be a cominon shell. 



Occurrence. — Oriskany Formation, Eidgely Member. Millers 

 Spring, Devil's Backbone, Maryland ; Warren Point, Pennsylvania. 



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



