72 RESEARCH IN CHINA. 
Genus OBOLELLA Billings. 
For discussion of genus see Monogr. U. S. Geol. Survey, vol. LI, 1912, pp. 
586-588. 
Obolella asiatica Walcott. 
Plate 3, Figures 4, 4a. 
Obolella asiatica WaLcorr, 1905, Proc. U.S. Nat. Mus., vol. xxvim, p. 297. (Described and discussed 
as below as a new species.) 
Obolella asiatica WatcoTt, 1912, Monogr. U.S. Geol. Survey, vol. L1, pp. 588-589, plate Lv, figs. 6, 6a. 
(A copy of the preceding reference.) 
General form broad, oval, with the ventral valve showing a tendency to become 
bluntly acuminate. Valves gently convex. Surface of shell marked by concentric, 
raised lines of growth that form the front edge of narrow lamelle of varying width; 
the raised lines are highest ontheir front side, which gives an imbricated appearance 
to the surface; fine, concentric striz occur on the interspaces between the raised 
lines. Shell strong, calcareous. 
The specimens occur in a compact, bluish-gray, oolitic limestone. None of 
them show the area or interior of the valves. The reference to Obolella is based on 
the general form and calcareous shell. The shells vary in size from 3 mm. to 5 mm. 
Obolella asiatica may be compared with young shells of O. crassa (Hall) [Orbicula ? 
crassa Hall, 1847, p. 290]. Its broadly elliptical form and slight convexity dis- 
tinguish it from other species of the genus. It may be that if material is found 
showing the interior of the valves the generic reference will be changed, but with 
the data now available the reference is to Obolella. 
w The geological horizon is in some doubt, as the specimens were found in a 
block of river-drift limestone. The associated fragments of trilobites are too indefi- 
nite for determination. Obolella is a Lower Cambrian genus, as far as known, and 
other blocks of river limestone at the same locality contained fragments of Olenellus, 
so the reference of the species is made to the Lower Cambrian. 
Since the publication of the above in 1905,’ a specimen has been found in the 
collections from the upper portion of the Man-t’o shales that locates the species 
in a limestone somewhere from go to 180 feet (27.4 m. to 54.8 m.) below the 
Ch’ang-hia formation. 
Formation and Locality.—Lower Cambrian: (C82’) A limestone bowlder col- 
lected in river drift 1 mile (1.6 km.) south of Chén-p’ing-hién, on the Nan-kiang 
River, southern Shen-si; also (C17), ferruginous limestone nodules in the brown 
sandy shales at the top of the Man-t’o shale [Blackwelder, 19074, p. 27 (list of fossils 
at top of page), and fig. 6 (bed 15), p. 25], at Ch’ang-hia, Shan-tung, China. 
Collected by Bailey Willis and Eliot Blackwelder. 
Genus YORKIA Walcott. 
Yorkia Walcott, 1897, Proc. U. S. Nat. Mus., vol. xrx, p. 714. (Described and discussed as a new 
genus.) 
For discussion of the genus Yorkia see Monogr. U. S. Geol. Survey, vol. 
Lisi 2s D101: 
Yorkia ? orientalis Walcott. 
Plate 3, Figures 5, 5a. 
Yorkia ? orientalis WALCOTT, 1906, Proc. U. S. Nat. Mus., vol. xxx, pp. 569-570. (Described and 
discussed as below as a new species.) 
Yorkia ? orientalis WaL,cort, 1912, Monogr. U.S. Geol. Survey, vol. LI, p. 612, plate Lxxxul, figs. 3, 3a. 
(A copy of the preceding reference.) 
This species is represented by a single small ventral valve, which has the external 
characteristics of Yorkia wanneri [Walcott, 1897b, p. 715, plate Lx, fig. 1], of the 

1Proc. U. S. Nat. Mus., vol. xxvii, 1905, p. 297. 
