DESCRIPTION OF PLATE 2. 
Obolus damesi (Walcott) (p. 65). 
1. Partly exfoliated ventral valve, showing main vascular sinuses and posterior portion of visceral 
area, X 6. U.S. Nat. Mus., Cat. No. 52529a. 
1a. Surface of inner layers of the shell of a ventral valve X 6. U.S. Nat. Mus., Cat. No. 52529). 
1b. Partly exfoliated dorsal valve, X 6. U.S. Nat. Mus., Cat. No. 52529¢. 
1c. Partial cast of the interior of a dorsal valve, X 6. U.S. Nat. Mus., Cat. No. 52529d. 
All of the specimens illustrated by figs. 1, 1a-c are from Locality C10, Middle Cambrian, Kiu-lung 
group, southwest of Yen-chuang, Shan-tung. 
1d. Enlargement to 2 diameters of a group of valves of this species lying on a parting of shaly limestone 
on which there are also numerous specimens of A crotreta shantungensts Walcott. Locality 35r, 
Middle Cambrian, Fu-chéu series, Liau-tung, Manchuria. U.S. Nat. Mus., Cat. No. 57737. 
1e. Flattened valves of this species, natural size, on argillaceous shale associated with Acrothele matthewi 
eryx Walcott. Locality 86d, Middle Cambrian, Fu-chou series, Liau-tung, Manchuria. U. 5. 
Nat. Mus., Cat. No. 57738. 
Obolus matinalis (Hall) ? (p. 65). 
2 (xX 4) and 2a (X 6). Ventral and dorsal valves of partly exfoliated shells. Locality C54, Upper 
Cambrian, Ch’au-mi-tién limestone west of Tsi-nan, Shan-tung. U.S. Nat. Mus., Cat. Nos. 
52533@ and 52533). 
Obolus minimus Walcott (p. 66). 
3. A partly exfoliated ventral valve, showing the cast of the visceral area and the main vascular 
canals, X 8. Locality C6, Middle Cambrian, Kiu-lung group limestone, south of Yen-chuang, 
Shan-tung. U.S. Nat. Mus., Cat. No. 52534a. 
3a. Exterior of associated dorsal valve, X 6. U.S. Nat. Mus., Cat. No. 525340. 
Obolus shansiensis Walcott (p. 67). 
4 and 4a. Partly exfoliated ventral valves, X 4. U.S. Nat. Mus., Cat. Nos. 52537a and 52538a. 
4b and 4c. Partly exfoliated and broken dorsal valves, X 4. U.S. Nat. Mus., Cat. Nos. 52537) 
and 52538). : 
The specimens represented by figs. 4 and 4b are from Locality C32, Middle Cambrian, Ki-sin-ling 
limestone, south of Chén-p’ing-hién, Shan-si; and figs. 4@ and 4c, Middle Cambrian, Ki-ch6éu lime- 
stone, south of Ting-hiang-hién, Shan-si. 
4d. Exfoliated ventral valve, X 4, showing edges of lamelle of the shell and radiating lines upon them. 
U. 8. Nat. Mus., Cat. No. 57743. 
4e. Enlargement to 3 diameters of a ventral and a dorsal valve in a limestone matrix. U.S. Nat. Mus., 
Cat. No. 57744. 
4f and 4g. Enlargement to 3 diameters of two ventral valves as they occur in the limestone matrix. 
U.S. Nat. Mus., Cat. No. 57742. 
The specimens represented by figs. 4d—g are from Locality 35r, Middle Cambrian, Fu-chéu series in 
limestone, Liau-tung, Manchuria. 
Obolus (Westonia) blackwelderi Walcott (p. 68). 
5 and 5a. Imperfect ventral valves. Locality C6. U.S. Nat. Mus., Cat. Nos. 52540a and 52540). 
5). Exterior of dorsal valve. Locality C2, Middle Cambrian, Kiu-lung group, south of Yen-chuang, 
Shan-tung. U.S. Nat. Mus., Cat. No. 52541. 
5c. Enlargement of the outer surface. U.S. Nat. Mus., Cat. No. 525400. 
Figures 5, 5a, and 5¢ represent specimens from Locality C6, Middle Cambrian, Kiu-lung group, south- 
west of Yen-chuang, Shan-tung. 
Lingulella marcia Walcott (p. 69). 
6. Summit view and side profile of exfoliated ventral valve, showing vascular markings and cast of 
concentric lines of growth, X 10. U.S. Nat. Mus., Cat. No. 57562. 
6a. View Ne a partly exfoliated dorsal valve, showing vascular markings, X 10. U.S. Nat. Mus., Cat. 
0. 57563. 
6b. View of exterior surface and side profile of a dorsal valve, X 10. U.S. Nat. Mus., Cat. No. 57745. 
6c and 6d. Interior of ventral valves, showing area and vascular markings, X 10. U.S. Nat. Mus., 
Cat. Nos. 57746 and 57747. 
6e and 6f. Interior of dorsal valves showing vascular markings, X 10. U.S. Nat. Mus., Cat. Nos. 
57748 and 57749. 
The specimens represented by figures 6, 6a—f are from Locality 35q, Middle Cambrian, Fu-chéu series 
in compact shaly limestone about 120 feet (36.5 m.) above Locality 3835p from which Lingulella 
manchuriensis comes, Province of Liau-tung, Manchuria. 
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