PLATE XI. 43 
OsoLus SHANSIENSIS Walcott (p. 415). 
Figure 7. Broad form of the ventral valve from Locality €32, Middle Cambrian river drift on the Nankiang, 1 mile 
south of Chonpinghien, Shensi, China. U.S. Nat. Mus. Cat. No. 52537a. 
7a. Narrow form of the ventral valve, the type specimen, from Locality €37, Middle Cambrian Kichou 
limestone, 8 miles south of Tinghianghien, Shansi, China. U.S. Nat. Mus. Cat. No. 52538a. 
7b. Broad form of the dorsal valve associated with the ventral valve represented by figure 7. U.S. Nat. Mus. 
Cat. No. 52537b. 
7c. Narrow form of the dorsal valve associated with the ventral valve represented by figure 7a. U.S. Nat. 
Mus. Cat. No. 52538b. 
Oxsotus Mryimus Walcott (p. 404). 
Figure 8. A partly exfoliated ventral valve, the type specimen, showing the cast of the visceral area and the main 
vascular canals. 
8a. Exterior of dorsal valve. 
The specimens represented are both from Locality €1, Middle Cambrian Kiulung limestone, 2 miles south of Yen- 
chuang, Sintai district, Shantung, China. U.S. Nat. Mus. Cat. Nos. 52534a and 52534b, respectively. 
OBoLus oBscuRUS Walcott (p. 406). 
Ficure 9. Interior of an imperfectly preserved dorsal valve, the type specimen. U.S. Nat. Mus. Cat. No. 52536a. 
9a. Exterior of an exfoliated, partly restored dorsal valve. U.S. Nat. Mus. Cat. No. 52536b. 
The specimens represented in figures 9 and 9a are both from Locality C63, Middle Cambrian sandy shale at the 
base of the Kiulung group, 3.5 miles southwest of Yenchuang, Sintai district, Shantung, China. 
Fiaure 9b. Partly exfoliated and broken ventral valve, showing concentric and radiating lines on the inner layers 
of the shell. U.S. Nat. Mus. Cat. No. 52535a. 
9c. Enlargement of the concentric strie of the exterior surface. U.S. Nat. Mus. Cat. No. 52535b. 
9d. Exterior surface of a broken dorsal valve. U.S. Nat. Mus. Cat. No. 52535c. 
The specimens represented in figures 9b-d are from Locality €75, Middle Cambrian limestone near the base of the 
Kichou formation, 4.5 miles south of Wutaihien, Shansi, China., 
