1S<) 



Distinguishing Characters.— Sub-circula r < >r transversely 

 sub-oval outline; nearly flat or slightly-concave pedicle 

 valve, becoming moderately convex near the beak: convex 

 brachial valve; large muscular area in the pedicle valve. 



/'. 



Fig. 91. Bhipidomella vanuxemi. Enlargement of surface striae: mold of interior of 

 pedicle valve : dorsal, ventral, lateral and cardinal views of a large and characteristic 

 specimen : interior of pedicle valve (from Hall ). 



A series of specimens shows considerable variation in out- 

 line, convexity, and character of muscular impressions 

 between the young and adult. 



Found in the lower live feet of Moscow shales, at Sections 

 4 and 5; in the Encrinal limestone, at Section 5, etc.; in 

 the Demissa bed and most of the beds below, at Sections ."i, 

 6, 7, 8. It is rare in the Trilobite beds, at. Section 8. 

 It is found in the shales down to the Pleurodictyum beds, 

 on the Lake Shore and in Avery's Creek. 



Rhipidomella leucosia. Hall. (Fig. 92.) (Pal. X. V.. 

 Vol. IV., p. 48, PL VII.) 



