190 



Distinguishing Characters. — Broadly ovate outline, with 

 jL»Teatest width below the middle; ]»()inted beak; convex 

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

 flattened toward the front; small areas; depression in the 

 center of the brachial valve. Readily distingnished from 

 R. vanuxenii by its more })ointed posterior end. 



f 



'^^ 



"'«akaai«Hi*«B»' 



Fig. '.I'-' i:h ,ii,:i.,i,,i Uii leucosia. Lateral and cardinal view: pedicle vahe nf another 

 specimen ; iuipression and interior of pedicle valves : ventral view of first specimen Cfroni 

 Hall;. 



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

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

 Avery's Ravine. 



Rhipii)omell.\ PENELOPE. Hall. (Fig. 93.) (Pal. N. Y., 

 Vol. IV., p. 50, PI. YI.) 



DistiugJiishhig Characters. — Large size; width greater 

 than length ; plano-convex transverse section ; regularly 

 convex brachial valve; flat or slightly concave pedicle valve, 

 which becomes somewhat convex near the beak ; striae 

 strongly arched upwards on the cardinal margin; muscular 

 area smaller and more rounded than R. vanuxenii. 



Found in the Encrinal limestone (fairly common), at 

 Section 5; Sticto})ora and Demissa beds (young?), at 

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

 Ravine. 



