68 RESEARCH IN CHINA. 
The form, surface markings, and shell structure are much like those of Obolus 
matinalis [p. 65] and O. tetonensis Walcott [1912b, plate 1x, figs. 5, 5a—d]. In outline 
O. shansiensis is more elongate than O. matinalis and less so than O. tetonensts. 
In Manchuria Prof. Joseph P. Iddings found this species to be abundant in the 
limestone and interbedded shale of the Dorypyge richthofeni zone. 
Formation and Locality——Upper Cambrian: (C87) Upper part of the Ki-chéu 
limestone (the fossils from this locality are not listed, but the presence of Cambrian 
strata at the locality is mentioned by Willis and Blackwelder [1907, p. 146]), in dense 
black limestone nodules in green-gray shales 10 feet (3 m.) below the base of the cliff 
limestone, 8 miles (12.8 km.) south of Ting-hiang-hién, Shan-si; and collected in 
(C32) Middle Cambrian; a fine-grained bluish-black limestone bowlder believed to 
have come from the lower part of the Ki-sin-ling limestone [Blackwelder, 1907¢c, 
p. 272], collected in river drift 1 mile (1.6 km.) south of Chon-p’ing-hién, on the 
Nan-kiang River, southern Shen-si, China. 
A specimen which is closely related, if not identical with this species, has been 
found (C71) in massive cliff-making limestone in the central portion of the Ki-chéu 
formation [Willis and Blackwelder, 1907, pp. 139 and 145 (second list of fossils)], 4 
miles (6.4 km.) southwest of Tung-yii, Shan-si, China. 
Collected by Bailey Willis and Eliot Blackwelder. 
Also (35r), Middle Cambrian: Fu-chéu series; limestones near the base of the 
series just above the white quartzite [see Blackwelder, 1907), p. 92, for general section 
giving stratigraphic relations]; collected in a low bluff on the shore of T'schang-hsing- 
tau Island, east of Niang-niang-kung, Liau-tung, Manchuria, China. 
Collected by J. P. Iddings and Li San. 
WESTONIA Walcott, subgenus of OBOLUS. 
For discussion of the subgenus Westonia see Monogr. U.S. Geol. Survey, vol. LI, 
I9I2, pp. 450-451. 
Obolus (Westonia) blackwelderi Walcott. 
Plate 2, Figures 5, 5a-—c. 
Obolus (Westonia) blackwelderi WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxv1u, p. 335. (Described 
and discussed as below.) 
Obolus (Westonia) blackwelderi WaLCcoTt, 1912, Monogr. U.S. Geol. Survey, vol. LI, p. 453, plate xxxIx, 
figs. 10, 10a—c. (A copy of the preceding reference.) 
General form elongate, with the width about one-half the length; front margin 
broadly rounded; sides slightly arched up to the lateral slopes, which are fairly 
straight in the ventral valve and curved toward the rounded posterior end of the 
dorsal valve; the beak of the ventral valve is pointed and marginal; the convexity 
of the valves is moderate, that of the dorsal apparently being the greater. Surface 
marked by concentric striz and lines of growth which are crossed by irregular, 
fine, imbricating, more or less transverse lines; the transverse lines trend slightly 
backward toward the sides of the valves. A ventral valve 8 mm. in length has a 
width of 5 mm. 
Nothing is known of the interior of the valves. When the shell is broken from 
the limestone, the outer surface usually adheres to the matrix. ‘The best exteriors 
are those of shells on the surface of the layers. Of the known species of Westonia, 
O. (W.) wimani Walcott [1912b, plate xLvut, figs. 5, 5a—b] and O. (W.) balticus Wal- 
cott [idem, plate xLvu1, figs. 7, 7a—-b] are most nearly related to O. (W.) black- 
welderi. ‘The latter isa larger shell and also less narrow proportionally where the 
gently arching sides pass into the postero-lateral slopes. 
