DESCRIPTION OF PLATE 2. 



Obolus damesi (Walcott) (p. 65). 



i. Partly exfoliated ventral valve, showing main vascular sinuses and posterior portion of visceral 



area, X 6. U. S. Nat. Mus., Cat. No. 525293. 



la. Surface of inner layers of the shell of a ventral valve X 6. U. S. Nat. Mus., Cat. No. 525296. 

 ib. Partly exfoliated dorsal valve, X 6. U. S. Nat. Mus., Cat. No. 52529^ 

 ic. Partial cast of the interior of a dorsal valve, X 6. U. S. Nat. Mus., Cat. No. 52529^. 



All of the specimens illustrated by figs, i, la-c are from Locality CIO, Middle Cambrian, Kiu-lung 

 group, southwest of Yen-chuang, Shan-tung. 



id. 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 Acrotreta shantungensis Walcott. Locality 35 r, 

 Middle Cambrian, Fu-chou series, Liau-tung, Manchuria. U. S. Nat. Mus., Cat. No. 57737. 



\e. Flattened valves of this species, natural size, on argillaceous shale associated with Acrolhele matlhewi 

 eryx Walcott. Locality 36(1, Middle Cambrian, Fu-chou series, Liau-tung, Manchuria. U. S. 

 Nat. Mus., Cat. No. 57738. 



Obolus matinalis (Hall) ? (p. 65). 



2 (X 4) and 20 (X 6). Ventral and dorsal valves of partly exfoliated shells. Locality C54, Upper 

 Cambrian, Ch'au-mi-tien limestone west of Tsi-nan, Shan-tung. U. S. Nat. Mus., Cat. Nos. 

 525330 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. 525340. 



30. Exterior of associated dorsal valve, X 6. U. S. Nat. Mus., Cat. No. 525346. 



Obolus shansiensis Walcott (p. 67). 



4 and 40. Partly exfoliated ventral valves, X 4. U. S. Nat. Mus., Cat. Nos. 525370 and 525380. 



46 and 4<r. Partly exfoliated and broken dorsal valves, X 4. U. S. Nat. Mus., Cat. Nos. 525376 

 and 525386. 



The specimens represented by figs. 4 and 46 are from Locality C32, Middle Cambrian, Ki-sin-ling 

 limestone, south of Chon-p'ing-hien, Shan-si; and figs. 40 and \c, Middle Cambrian, Ki-chou lime- 

 stone, south of Tiug-hiang-hien, Shan-si. 



4</. Exfoliated ventral valve, X 4, showing edges of lamellae of the shell and radiating lines upon them. 



U. S. Nat. Mus., Cat. No. 57743. 

 4. Enlargement to 3 diameters of a ventral and a dorsal valve in a limestone matrix. U. S. Nat. Mus., 



Cat. No. 57744- 

 4/ 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. $d-g are from Locality 35 r, Middle Cambrian, Fu-chou series in 

 limestone, Liau-tung, Manchuria. 



Obolus (Westonia) blackwelderi Walcott (p. 68). 



5 and 50. Imperfect ventral valves. Locality C6. U. S. Nat. Mus., Cat. Nos. 525400 and 525406. 

 56. Exterior of dorsal valve. Locality 02, Middle Cambrian, Kiu-lung group, south of Yen-chuang, 



Shan-tung. U. S. Nat. Mus., Cat. No. 52541. 

 50. Enlargement of the outer surface. U. S. Nat. Mus., Cat. No. 525401;. 



Figures 5, 50, and 50 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. 

 da. View of a partly exfoliated dorsal valve, showing vascular markings, X 10. U.S. Nat. Mus., Cat. 



No. 57563. 



66. 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 6/. 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-/ are from Locality 35 q, Middle Cambrian, Fu-chou series 

 in compact shaly limestone about 120 feet (36.5 m.) above Locality 35 p from which Lingulella 

 manchuriensis comes, Province of Liau-tung, Manchuria. 



232 



