194 



Distinguishing Characters. — Hinge line shorter than the 

 grea.tes1 width of the shell ; extremities rounded ; length and 

 width about as two to three; surface striae distant. 



Found in ili«- StiGtopora and Demissa beds, at Section f> 

 (rare); in t lie shale below the Athyris spiriferoides bed. at 

 Section 7 (rare); and in the Pleurodictyum beds, in Avery's 

 Ravine i rare). 



Genus STROPHEODONTA. Hall. 



I Kty : Stropli&u*, hinge ; odous, tooth.] 

 (1852: Pal. X. Y., Vol. II., p. 63. 1892: Pal. X. Y.. Vol. VIII., Pt. I., p. 284.) 



Shell concavo-convex, the convex valve being the pedicle 

 valve. Outline varying from semi-circular to semi-elliptical, 

 with the hinge line usually equal to or greater than the greatest 

 width of the shell. Areaof the pedicle valve higher than that 

 of the brachial valve, both margins furnished with project- 

 ing: denticulations. which interlock and form articulations. 

 Muscular areas well marked and variously bounded. A 

 strongly marked, commonly bifid, cardinal process occurs in 

 the brachial valve. 



A number of sub-genera are recognized. 



Stroimikodonta demissa. Conrad. (Fig. 98.) (Pal. N.Y., 

 Vol. IV. ; p. 101, PL XVII.) 



Distinguishing Characters. — Medium size: pedicle valve 

 strongly con vex ; concavity of the brachial valve less: length 

 and width nearly equal; surface stria" numerous, stronger 

 and more elevated near the beak, increasing by intercalation 

 and bifurcation towards the front; muscular impressions of 

 the pedicle valve consist of large Habellate divaricntors, 

 separated towards the front and distinctly lobed. and small 

 adductors lying between them separated from each other by 

 a depression : in the brachial valve the adductor impressions 

 are divided longitudinally by a narrow ridge, and often 

 limited in front by elevated ridges. 



Found in the Enerinal limestone, at Section 5 (one speci- 

 men): the Stictopora bed, a1 Sections 5 and 6 (rare); the 



