PLATH LXTX. . 233 
ACROTRETA SHANTUNGENSIS Walcott (p. 710). 
Figures 5, 5a, and 5b. Top, side, and back views of a ventral valve, the type specimen. U.S. Nat. Mus. Cat. 
No. 52512a. 
5c. Top view of a ventral valve with the apex broken off. U.S. Nat. Mus. Cat. No. 525121 
5d. Exterior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52512c. 
5e. Interior of a dorsal valve. U.S. Nat. Mus. Cat. No. 52512d. 
D. 
The specimens represented are all from Locality €62, Middle Cambrian limestone 2.5 miles south of Yenchuang, 
Sintai district, Shantung, China. 
ACROTRETA PACIFICA Walcott (p. 699). 
Fiaures 6 and 6a. Top and side views of an elevated ventral valve, the type specimen, from Locality €5, Middle 
Cambrian limestone 3.2 miles southwest of Yenchuang, Sintai district, Shantung, China. U. S. Nat. 
Mus. Cat. No. 52506a. 
6b, 6c, and 6d. Top, back, and side views of a ventral valve with pointed apex, associated with the specimen 
represented by figures 6 and 6a. U.S. Nat. Mus. Cat. No. 52506b. 
6e. Partly exfoliated dorsal valve from Locality €2, Middle Cambrian limestone 2 miles south of Yen- 
chuang, Sintai district, Shantung, China. U.S. Nat. Mus. Cat. No. 52508a. 
