198 



Found ill the lower Moscow shales, at Sections -4 and .') 

 (coininon) ; Encrinal limestone, at Section ."> (coniinoii); 

 Stictopora and Demissa beds, at Section 5 (coinnion) ; shales 

 between the Demissa and Triiobite beds, at Sections G and 7 

 (frequent) ; Triiobite beds, at Section S, and in Averv's Creek 

 (rare) ; shales below the Triiobite beds, on the Lake Shore 

 and in Avery's Creek (occasionally) ; Pleurcjdictyum beds, in 

 Avery's Ravine (rare); shale below the Nautilus bed (not 

 uncommon). 



Stkopheodoxta ( DoxviLLiXA ) ix.KQnsTRiATA. (Courad.) 

 (Fio-. 101.) (Pal. X. Y., Vol. IV.. p. 100, PI. XVIII.) 



Distinguishing- diameters. — Small size; considerable con- 

 vexity of pedicle valve; extended hinge line with acute, 

 sometimes auriculate, extremities ; surface marked 1)V distant 



> 



p^JJ^^^St*?^'" 





Fig. 101. Stropheodonta incequititriata. Lateral and dorsal views of two specimens; 

 three pedicle valves: interior of a brachial valve, showing cardinal process and muscular 

 impressions (from Hall ). 



strise, with finer, almost invisible, stria? between ; in the 

 brachial valve the bifid cardinal process is supported by a 

 ridge, which divides anteriorly and encloses a muscular area, 

 for the attachment of the anterior adductors. 



Found in the Moscow shales, three to five feet above the 

 base, at Sections 4 and 5 (common); Encrinal limestone, at 

 Section 5 (rather rare); Stictopora bed, at Section 5 (fre- 

 quent); Demissa bed, at Section 5 (very common) ; Triiobite 

 beds, at Section 8, and on the Lake Shore (occasionally) ; 

 shale and limestones between the Triiobite and Strophalosia 

 beds, on the Lake Shore and in Avery's Creek (occasionally). 



