190 



Distinguishing Characters. — Broadly ovate outline, with 

 greatest width below the middle; pointed beak; convex 

 brachial and pedicle valves, the latter the less convex, and 

 flattened inward the front; small areas: depression in the 

 center of the brachial valve. Readily distinguished from 

 R. vanuxemi by its more pointed posterior end. 







FlG. !i2. Tthipidomella leucosia. Lateral and cardinal view: pedicle valve of another 

 Bpecimen : impression and interim- of pedicle valves : ventral view of first specimen (from 

 llalh. 



Found in the Encrinal limestone (rare), at Section 5; in 

 the shale below the Trilobite beds, on the Lake Shore and in 

 Avery's Ravine. 



Rhipidomella penelope. Hall. (Fig. 93.) (Pal. N. Y., 

 Vol. IV.. p. 50, PL VI.) 



Distinguishing Characters. — Large size; width greater 

 than length; plano-convex transverse section; regularly 

 convex brachial valve; fi;il or slightly concave pedicle valve, 

 which becomes somewhat convex near the beak; stria- 

 Btrongly arched upwards on the cardinal margin; muscular 

 area smaller ami more rounded than R. vanuxemi. 



Found in the Encrinal limestone (fairly common), at. 

 Section 5; Stictopora and Demissa beds (young?), at 

 Section 5; in the shale below the Trilobite beds, in Avery's 

 Ravine. 



