PLATE XCVI. 321 
PLECTORTHIS JAMEsI (Hall) (p. 772). 
Figure 5. Exterior of a ventral valve. U.S. Nat. Mus. Cat. No. 51307a. 
5a. Interior of a ventral valve. U.S. Nat. Mus. Cat. No. 51367b. 
5b. Interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 51307c. 
5¢e. View of the interior of the specimen represented by figure 5b over the front margin so as to obtain a front 
view of the cardinal process and crural plates. 
The specimens represented are all from Ordovician beds of Lorraine age at Cincinnati, Ohio, and the figures are 
introduced here for comparison. 
PLECTORTHIS PARVA (Dalman) (p. 776).4 
Ficure 6. Exterior of a ventral valve, to illustrate form and surface ribs. U.S. Nat. Mus. Cat. No. 52314a. 
6a-d. Side views of four specimens having the two valves united, to illustrate the variation in the convexity 
of young and adult shells. U.S. Nat. Mus. Cat. Nos. 52314b-e, respectively. 
6e. Interior of a ventral valve. U.S. Nat. Mus. Cat. No. 52314f. 
6f. Interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52314¢. 
6g. Enlargement of the posterior portion of the interior of a dorsal valve, to show the small cardinal process, 
etc. U.S. Nat. Mus. Cat. No. 52314h. 
The locality and horizon of the specimens represented are unknown. 
aSee Zoorthis christianiz, p. 776. 
62667°—vot 51, pr 2—12 21 
