344 Bepoet of the State Geologist. 



Width of the original specimen along the hinge, 23 mm.'; 

 greatest length, 19 mm. 



Trenton limestone. Jachsonburg^ ]^. Y. 



Strophomena Winchelli. 

 Plate 4, figs. 81-33. 



Strophomena nutans, Hall. Rept. State Geologist N. Y. for 1882, expl. pi. (ix) 



39, figs. 10, 12-14. 1883. 

 Strophomena Winchtlli, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 



344, pi. ix, figs. 10, 12-14, and pi. xx, fig. 26, 1892. 



Shell elongate semiovate ; strongly convexo-concave. Hinge- 

 line straight and making the greatest diameter of the shell. 

 Cardinal angles sometimes extended. Pedicle-valve with a 

 moderately broad area and deltidium ; apex slightly elevated, the 

 valve becoming deeply concave over the pallial region and 

 reflected at the margins. The teeth are strong and divergent, 

 and from their bases extend elevated curving ridges which form 

 the margin of the subcircular or subovate muscular area. 

 Diductor scars broad, inclosing an elongate and narrow adductor. 

 Within the anterior and lateral margins of the valve is a thick- 

 ened ridge which is crossed by branches of the vascular sinuses. 

 Brachial valve flat in the umbonal region, very convex over the 

 median portion and sloping gradually to the margins. The car- 

 dinal process consists of two slender and short apophyses which 

 are united at their base with the crural plates. The latter are 

 very divergent and extend in a broad curve subparallel to the 

 hinge-line. The muscular scars consist of two pairs, the posterior 

 being broad and striated, the anterior narrow and close to the 

 median line. The members of the pairs are separated by a low 

 median ridge. Surface of the shell covered with numerous very 

 fine filiform strisG, regularly but not conspicuously alternating in 

 size. Delicate concentric striae are sometimes discernible. 



Trenton horizon. Clifton and Janeeville^ Wiscojisin. 



This shell has been referred to the Hemipronites nutans^ James 

 (Meek), of the Hudson Kiver group, which it resembles in' its 

 general expression. It differs from this species in its internal 

 characters and more finely and abundant striated exterior. 



