66 RESEARCH IN CHINA. 
Obolus matinalis (Hall)? Wa.cott, 1905, Proc. U. S. Nat. Mus., vol. xxvu1, p. 325. (Mentioned as 
below. Doubtfully identifies the species from China.) 
Obolus matinalis (Hall)? WaLcott, 1912, Monogr. U. S. Geol. Survey, vol. LI, p. 402, plate vu, figs. 
3 and 3a. (Copy of preceding reference.) 
A form indistinguishable from this species occurs in a gray limestone of Upper 
Cambrian age. Only the general form of partly exfoliated shells is known. 
Formation and Locality—Middle Cambrian: (C54) Lower part of Ch’au-mi- 
tién limestone [Blackwelder, 1907a, p. 42 (part of last list of fossils)], near top of 
limestone knoll two-thirds of a mile (1.1 km.) west of Tsi-nan, Shan-tung, China. 
Collected by Eliot Blackwelder. 
Fragments of a similar shell were found in the (C67) stream gravels used in 
making the railroad grade west of the west city gate at Tsi-nan. 
Collected by Eliot Blackwelder. 
Obolus minimus Walcott. 
Plate 2, Figures 3, 3a. 
Obolus minimus WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvim, p. 325. (Described as below as a 
new species.) 
Obolus minimus WALCOTT, 1912, Monogr. U.S. Geol. Survey, vol. Lt, pp. 404-405, plate x1, figs. 8 and 8a. 
(Copy of the preceding reference.) 
This is a small shell of the general form of Obolus shansiensis [p. 67]. The 
ventral valve is obtusely acuminate and the dorsal nearly circular; valves gently 
convex. Surface marked by rather strong, concentric lines of growth and numerous 
very fine, concentric strie. The inner layers of shell are shiny black and orna- 
mented with numerous fine, radiating striz and concentric lines. Shell built up of 
several thin layers or lamelle that form a shell which is thin over the umbonal region 
and gradually thickens toward the front and side margins, as the short oblique 
lamella become more numerous. ‘The three specimens in the collection average 3 
mm. in transverse diameter; the ventral is a little longer than the dorsal valve. 
A partly exfoliated ventral valve shows a well-marked visceral area, extending 
forward about one-third of the length of the shell; also narrow main vascular sinuses 
starting near the apex and extending obliquely forward well into the valve, about 
midway between the median line of the valve and the lateral margins. 
This neat little shell is distinguished by its nearly circular outline, low con- 
vexity, and small size. 
Formation and Locality—Middle Cambrian: (C1) Lower shale member of 
the Kiu-lung group [Blackwelder, 1907a, pp. 37 and 4o (part of the third list of 
fossils), and fig. 10 (bed 4), p. 38], 2 miles (3.2 km.) south of Yen-chuang, Sin-t’ai 
district, Shan-tung, China. 
Collected by Eliot Blackwelder. 
Obolus obscurus Walcott. 
Plate 1, Figures 12, 12a-d. 
Obolus obscurus WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvii, p. 326. (Described and discussed 
essentially as in the first two paragraphs below as a new species.) 
Obolus obscurus WALCOTT, 1912, Monogr. U.S. Geol. Survey, vol. L1, pp. 406-407, plate x1, figs. 9, ga—d, 
(Described and discussed essentially as below.) 
This species is represented by one interior of a small dorsal valve which is very 
distinctive, the exterior of a crushed dorsal valve, and numerous fragments of the 
shell scattered through the hard, dark gray, shaly sandstone. The large dorsal 
valve has a length of 9 mm., width 7 mm. The shell is strong and marked on its 
