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, 43. 

 Obolella asiatica WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxvin, p. 297. (Described and discussed 



as below as a new species.) 



Obolella asiatica WALCOTT, 1912, Monogr. U. S. Geol. Survey, vol. LI, pp. 588-589, plate LV, figs. 6, 60. 

 (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 lamella? of varying width; 

 the raised lines are highest on their front side, which gives an imbricated appearance 

 to the surface; fine, concentric striae 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 0. crassa (Hall) [Orbicula 1 

 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. 



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 Maii-t'o shales that locates the species 

 in a limestone somewhere from 90 to 180 feet (27.4 m. to 54.8 m.) below the 

 Ch'ang-hia formation. 



Formation and Locality. Lower Cambrian: (C32') A limestone bowlder col- 

 lected in river drift i mile (1.6 km.) south of Chon-p'ing-hien, 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, 19070, 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. xix, p. 714. (Described and discussed as a new 

 genus.) 



For discussion of the genus Yorkia see Monogr. U. S. Geol. Survey, vol. 

 Li, 1912, p. 61 1. 



Yorkia ? orientalis Walcott. 



Plate 3, Figures 5, 50. 

 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 WALCOTT, 1912, Monogr. U.S. Geol. Survey, vol. LI, p. 612, plate LXXXII, figs. 3,30. 

 (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, 18976, p. 715, plate LX, fig. i], of the 



'Proc. U. S. Nat. Mus., vol. xxvin, 1905, p. 297. 



