68 RESEARCH IN CHINA. 



The form, surface markings, and shell structure are much like those of Obolus 

 niatittalis [p. 65] and O. tetonensis Walcott [19126, plate ix, figs. 5, sa-d}. In outline 

 O. shansiensis is more elongate than 0. matinalis and less so than 0. tetonensis. 



In Manchuria Prof. Joseph P. Iddings found this species to be abundant in the 

 limestone and interbedded shale of the Dorypyge richthofcni zone. 



Formation and Locality. Upper Cambrian: (037) Upper part of the Ki-chou 

 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 in. ) below the base of the cliff 

 limestone, 8 miles (12.8 km.) south of Ting-hiang-hien, Shan-si; and collected in 

 (032) Middle Cambrian; a fine-grained bluish-black limestone bowlder believed to 

 have come from the lower part of the Ki-sin-ling limestone [Blackwelder, igojc, 

 p. 272], collected in river drift i mile (1.6 km.) south of Chon-p'ing-hien, on the 

 Nan-kiang River, southern Shen-si, China. 



A specimen which is closely related, if not identical with this species, has been 

 found (071) in massive cliff-making limestone in the central portion of the Ki-chou 

 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 (35 r). Middle Cambrian: Fu-chou series; limestones near the base of the 

 series just above the white quartzite [see Blackwelder, 19076, p. 92, for general section 

 giving stratigraphic relations] ; collected in a low bluff on the shore of Tschang-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, 

 1912, pp. 450-451. 



Obolus (Westonia) blackwelderi Walcott. 

 Plate 2, Figures 5, $a-c. 



Obolus (Westonia) blackwelderi WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxvni, p. 335. (Described 



and discussed as below.) 

 Obolus (Westonia) blackwelderi WALCOTT, 1912, Monogr. U.S. Geol. Survey, vol. Li, p. 453, plate xxxix, 



figs. 10, \oa-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 striae 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, 

 0. (W.) iL'imani Walcott [19126, plate XLVIII, figs. 5, 50-6] and O. (W.) balticus Wal- 

 cott [idem, plate XLVIII, figs. 7, ja-b] are most nearly related to 0. (IV.) black- 

 welderi. The latter is a larger shell and also less narrow proportionally where the 

 gently arching sides pass into the postero-lateral slopes. 



