78 RESEARCH IN CHINA. 



ican Pacific Province species of Acrotreta it most nearly approaches .-1. idahoensis 

 Walcott [19126, plate LXV, figs, i, la-i; plate LXVIII, figs. 2, 2a-g] in the external 

 form of the valves. The vascular markings on the interior of the dorsal valve 

 differ in detail, as may be seen by comparing them. 



Formation and Locality. Middle Cambrian: (35 q) Fu-chou series; about 200 

 feet (61 m.) above the white quartzite [see Blackwelder, 19076, p. 92, for general 

 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. 



Acrotreta sp. undt. 



In the Upper Cambrian limestone a single dorsal valve has been found at each 

 of two localities (056 and 068) that resembles the dorsal valve of A. pacifica, 

 [p. 75] but in the absence of ventral valves I shall not attempt to identify them with 

 any described species from the Middle Cambrian, or describe as new species. 



Formation and Locality. Middle Cambrian: (056) Lower part of Ch'au- 

 mi-tien limestone, 25 feet below the top of Pagoda Hill [Blackwelder, 19070, p. 42 

 (part of last list of fossils)], i mile (1.6 km.) west of Tsi-nan, Shan-tung, and (068) 

 upper part of the Ch'au-mi-tien limestone [idem, p. 36 (part of third list of fossils)], 

 on crest of ridge east of Ch'au-mi-tien, 200 yards (183 m.) north of the wayside 

 shrine, Ch'ang-hia district, Shan-tung, China. 



Collected by Eliot Blackwelder and Li San. 



Genus DISCINOPSIS Matthew. 



Discinopsis (Matthew MS.) HALL and CLARKE, 1892, nth Ann. Rept. State Geologist New York for 



1891, pp. 250-251. (Described.) 

 Discinopsis Matthew, HALL and CLARKE, 1892, 45th Ann. Rept. New York State Museum for 1891, 



pp. 566-567. (Copy of preceding reference.) 

 Discinopsis Matthew, HALL and CLARKE, 1892, Nat. Hist. New York, Paleontology, vol. vm, pt. i, 



pp. 105-106. (Described and discussed as a new genus.) 

 Discinopsis Matthew, WALCOTT, 1908, Smithsonian Misc. Coll., vol. LIII, No. 4, plate xi, and pp. 142 



and 146. (Classification of genus.) 

 Discinopsis Matthew, WALCOTT, 1912, Monogr. U. S. Geol. Survey, vol. Li, p. 720. (The original 



description of Acrotreta. I gulielmi is copied and the genus is discussed under Discinopsis gulielmi, 



pp. 720-721). 



Discinopsis gulielmi (Matthew). 



The original diagnosis of the genus by Matthew was combined with that of 

 the type species, Acrotreta ? gulielmi, as follows: 



"Shell subcircular in outline. Surface depressed-conical, apices eccentric, not 

 marginal. Pedicle valve with the apex truncated by a circular foraminal aperture ( ?) . 

 The interior of this valve is characterized by a pair of deep, diverging furrows, 

 passing forward from the beak or internal foraminal opening, in broad curves 

 which converge toward the anterior margin but without meeting. These furrows 

 enclose a thickened and .somewhat elevated central area, which in the subumbonal 

 region is apparently free, projecting for a short distance, like a narrow, triangular 

 shelf, beneath which the foramen probably opened. The interior opening of the 

 foramen is, however, not apparent on any of the specimens examined, for, as usually 

 preserved, the matrix has adhered to this subapical cavity, and in a single example 

 only is the shelf-like character of the median area distinctly demonstrated. A faint 

 longitudinal ridge passes from the apex of the shelf to the anterior margin, but no 

 other markings are discernible on the interior except faint radiating or slightly 

 undulating, probably vascular lines. 



