ISO 



Distwguish in^i^- Cli;i rn cters.— Sii 1 )-ei rcula r or trans versely 

 sub-oval outline; nearly Hat or sli<ihtly-conca,ve pedicle 

 valve, becoming- moderately convex near the beak; convex 

 brachial valve; laroe mnscnlar area in the pedicle valve. 



\j-\ 



Fig. 91. Rhipidomella vanuxemi. Enlargement of siirfari- siii;i'; in.ild .if interior of 

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

 specimen ; interior of pedicle valve (from Hall J. 



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 five 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 5, 

 0, 7, 8. It is rare in tlie Trilobite beds, at Section S. 

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

 on the Lake Shore and in Aveiy's Creek. 



Rhipidomella leucosia. Hall. (Fig. 92.) (Pal. N. Y., 

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



