Maryland Geological Survey 319 



va.'icularia, i. e., tlie narrower muscular impressions of the dorsal valve, 

 has no partieuhir significance, since that grades into the wider muscular 

 area of S. rnagnlfica. S. lincklcvni is a smaller species with a flatter dorsal 

 valve and a septum se])arating the posterior pair of adductor muscles. 



Length about 5 cm. ; width about 6 cm. 



Occurrence. — Ohiskanv Formation, Eidgely Member. Knobly 

 Mountain, Miller's Spring near Cumberland, Devil's Backbone, Martin 

 Mountain, Collier's Eun, Maryland; Warren Point, Pennsylvania; Pen- 

 dleton County, West Virginia. 



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



Stropheouonta (Leptostropitia) magniventra Hall 

 Plate LVIII, Figs. 6-8 



Strophodonta magniventra Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. 



Nat. Hist., p. 54. 

 Strophodonta magniventra Hall, 1859, Nat. Hist. N. Y. Pal., vol. iii, p. 411, 



pi. xcii, figs. 2a-2c, 3; pi. xcv, fig. 9, ISGl. 

 ? Strophodonta linckhrni Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, pi. xciii, 



fig. 2a (not figs. 3a. 3b = S. linckJfrni). 

 Strophodonta vascularia Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, pi. xciii, 



figs. 2&, 2c (not pi. xcii, fig. 4; pi. xcv, fig. 10^«Sf. magniflca) , ISGl. 

 Strophomena magniventra Billings, 1861, Can. Jour. Sci. Arts, vol. vi, p. 349. 

 Strophomena magniventra Billings, 1863, Geol. Canada, p. 961, fig. 469. 

 Strophomena magnive^itra Billings, 1874, Pal. Foss., vol. ii, p. 22, figs. 10-12, 



pi. ii, figs. 2, 2a. 

 Stropheodonta (Leptostrophia) magniventra Hall and Clarke, 1892, Nat. 



Hist. N. Y., Pal., vol. viii, pt. i, p. 288, pi. xiii, figs. 25, 26. 

 ? Stropheodonta lincklwni Clarke, 1900, Mem. N. Y. State Mus., vol. iii. No. 3, 



p. 52, pi. vii, fig. 37. 



Description. — " Shell suhsemicircular varying to longitudinally sub- 

 oval, variable ; length usually two-thirds the breadth, sometimes equal or 

 greater: ventral valve convex in the central and umbonal regions, flattened 

 towards the extremities ; beak slightly incurved ; cardinal border sloping 

 from the umbo : dorsal valve unknown, probably concave : hinge-line cren- 

 ulated, equal to the greatest width of the shell, sometimes extended into 

 mucronate points beyond the lateral margins of the shell ; area of ventral 

 valve very broad, slightly curved, distinctly marked by vertical striae pro- 

 duced by the prolongation of the crenulations of the hinge; foramen 



