316 Systematic Paleontology 



This species is readily separated from S. leckii by its finer and equal 

 rounded radial strige, while the concentric corrugations, if present at all, 

 are very faint. 



Occurrence. — Helderberg Formation, Coeymans Member. Dawson, 

 Corriganville. New Scotland Member. Dawson, Devil's Backbone, 

 Corriganville. Becraet Member. Washington County, Maryland. 

 Warren Point, Pennsylvania. 



Collection. — Maryland Geological Survey. 



Stropheodonta (Leptostrophia) bipartita (Hall) 



Plate LYIT, Figs. 17, 18 



Leptwna bipartita Hall, 1858, Pal. N. Y., vol. ii, p. 326, pi. Ixxiv, figs. 4, 5. 

 Stropheodonta nearpassi Schuchert, 1897, Bull. U. S. Geol. Survey, No. 87, 



p. 427. 

 Stropheodonta textilis Schuchert, 1897, Bull. U. S. Geol. Survey, No. 87, p. 



427. 

 Strophomena (?) bipartita Schuchert, 1897, Bull. U. S. Geol. Survey, No. 87, 



p. 429. 

 Stropheodonta bipartita Weller, 1903, Pal. N. J., vol. iii, p. 226, pi. xx, figs. 1-5. 



Desc7'iption. — " Shell with thin, nearly flat brachial valve and slightly 

 convex pedicle valve, longitudinally subsemielliptical in outline, the 

 hinge-line produced beyond the body of the shell into mucronate exten- 

 sions, hinge-line crenulate. 



" Surface of both valves marked by fine, irregularly alternating, angular, 

 raised striae, which are not continuous over the umbo to the beak, and 

 which curve outward on the sides of the shell in passing to the margin, 

 the curvature becoming stronger on approaching the hinge-line. The sur- 

 face is also marked by much finer, crowded, concentric lines, which con- 

 tinue to the beak. Oblique wrinkles along the cardinal margin are 

 present in many specimens. The interior of the valves, more especially 

 the pedicle, is covered with fine, closely crowded papillae, which gives to 

 the surface of internal casts a finely pitted or punctate appearance. These 

 internal papillae may frequently be detected through the thin shell sub- 

 stance as dark spots, giving it a punctate appearance, but there are ap- 

 parently no perforations. The muscular impressions of the pedicle valve 



