76 RESEARCH IN CHINA. 



Two specimens of the ventral valve of this species are figured. One of these 

 has a slightly transverse, broadly oval base, and a more definite false area. The 

 species is closely related to Acrotreta idahoensis alta Walcott [191 2b, p. 689, plate LXV, 

 figs. 4, 4a-b], except that the ventral valve is not quite so elevated. 



Acrotreta pacifica occurs in large numbers in a hard shale and shaly limestone in 

 southwestern Manchuria. It is associated with Dorypyge richthofeni both in Shan- 

 tung and Manchuria. 



Formation and Locality. Middle Cambrian: (0 1 and 02) Lower shale member 

 of the Kiu-lung group [Blackwelder, 19070, pp. 37 and 40 (part of the third list of 

 fossils), and fig. 10 (beds 4 and 5), p. 38], 2 miles (3.2 km.) south of Yen-chuang; 

 also (04), limestone nodules at the base of the lower shale member of the Kiu-lung 

 group [idem (second list of fossils), and fig. 10 (bed 4), p. 38], 3 miles (4.8 km.) south- 

 west of Yen-chuang, and (05) lower limestone member of the Kiu-lung group, idem, 

 pp. 37 and 39 (first list of fossils), and fig. 8a (bed 30), p. 29], 3.2 miles (5.1 km.) 

 southwest of Yen-chuang, and (012) gray limestone near the top of the middle lime- 

 stone member of the Kiu-lung group [idem, pp. 37 and 41 (part of the first list), and 

 fig. 10 (bed 7), p. 38], 3.25 miles (5.2 km.) southwest of Yen-chuang, Sin-t'ai district, 

 Shan-tung, China. 



Collected by Eliot Blackwelder and Li San. 



Also (35p), Fu-chou series; shales about 80 feet (24 m.) above the white quartz- 

 ite [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. 



A single dorsal valve similar in outline to those of this species as found in Man- 

 churia (35 p) occurs in the Ch'ang-hia formation, Locality 024. It may be com- 

 pared but not identified with A. pacifica, as the dorsal valves of many of the species 

 of Acrotreta are very much alike. 



This dorsal valve is from Locality 024, Middle Cambrian, near the top of 

 the black oolite group in the uppermost layers of the Ch'ang-hia formation [Black- 

 welder, 19070, p. 33, part of last list of fossils], 2 miles (3.2 km.) east of Ch'ang-hia, 

 Shan-tung, China. 



Collected by Eliot Blackwelder. 



Acrotreta shangtungensis Walcott. 

 Plate 4, Figures 2, 2<z-c. 



Acrotreta shantnngensisWALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxvin, pp. 301-302. (Described 



and discussed as below as a new species.) 

 Acrotreta shantitngensis WALCOTT, 1912, Monogr. U. S. Geol. Survey, vol. LI, pp. 710-711, plate i.xix, 



figs. 5, 50-e. (A copy of the preceding reference.) 



Shell small. Ventral valve a low cone with the apex a little forward of the pos- 

 terior margin, which is slightly flattened; apex minute, directed backward and pro- 

 jecting slightly over the faintly defined false area. The cast of the interior shows 

 that the apical callosity was rather large and the main vascular sinuses were well 

 defined on each side of it; the cardinal scars are small and not prominent. 



Dorsal valve slightly convex ; apex marginal ; surface marked by a rather broad, 

 shallow median depression that begins on the umbo and gradually widens toward the 

 front margin. The interior of the dorsal valve has a strong median ridge extending 

 from the posterior margin two-thirds the distance toward the front; a small, elevated 

 cardinal scar occurs on each side of the median ridge a little in advance of the pos- 



