252 SYSTEMATIC PALEONTOLOGY 



STROPHOMENA SINUATA James 



Plate LIV," Figs. 10-14 



Strophomena sinuata James, 1871, Cat. Fossils, Cincinnati group, p. 9. 

 Strophomena (Hemipronites) sinuata Meek, 1873, Pal. Ohio, vol. i, p. 87, 



pi. 15, fig. 5a-g. 

 Strophomena sinuata Foerste, 1912, Bull. Sci. Lab. Denison Univ., vol. xvii, 



p. 57, pi. i, figs. 3a-d. 



Description. " Shell semicircular, or forming rather more than a 

 semicircle, moderately convex, with valves nearly equal, the dorsal being 

 most convex in the central and anterior regions, and the ventral near 

 the Timbo; hinge nearly or quite equalling the greatest breadth; lateral 

 margins forming more or less nearly right angles with the hinge line; 

 or sometimes rounding a little to the same, and rounding regularly to the 

 front, which forms a semicircular curve, with rarely a slight sinuosity 

 at the middle. 



" Dorsal valve, flat at the beak, which is not distinct from the cardinal 

 margin, usually a little raised in the middle at the front, so as to form a 

 low, broad, undefined medial prominence; cardinal area narrow and 

 inclined backward; interior with a low, small, deeply bipartite cardinal 

 process, from which diverge three small ridges, the two lateral of which 

 extend obliquely outward to form the margins of the rather well-defined 

 sockets for the reception of the teeth of the other valve, while the third 

 ridge is central, and extends a short distance forward; muscular scars 

 not visible in any specimen examined. 



"Ventral valve moderately convex at the umbo, which is not very 

 prominent or arched, and has a minute perforation at the apex; front 

 with usually a broad, shallow, undefined depression ; lateral regions more 

 or less nearly flat; cardinal area well developed, tapering to the lateral 

 extremities, flat, and inclined more or less obliquely backward ; foramen 

 closed by a prominent, triangular deltidium; interior showing small, 

 somewhat saucer-shaped cavity, formed by the low, sharp dental laminae, 

 extending forward from the inner side of the rather well-developed 

 oblique cardinal teeth, and curving a little toward each other, without 



