CAMBRIAN FA UNAS OF CHINA— WALCOTT. 569 



b}' a small, circular foraminal aperture. In front of the cast of the 

 base of the foraminal aperture there is a l»road depression that extends 

 to the front margin; on each side of the central depression an elongate, 

 slightly depressed area extends forward and outward from near the 

 ])ase of the cast of the foraminal aperture, along the ridge on each side 

 of the median depression; ])ack of the base of the foraminal aperture 

 there is a narrow, short, arched furrow that indicates the presence of 

 a corresponding ridge on the interior of the shell. No other mark'ngs 

 are shown on the cast, except the faint outline of what ma}^ have been 

 the visceral area, on the median line in front of the base of the forami- 

 na! aperture and between the broad vascular sinuses. 



Observations. — This species is referred to the genus Dlscinopsis as 

 the result of comparison with specimens of the interior of a ventral 

 valve of D. guUelmi. One interior of the latter species has scars much 

 like those in D. sulcatus. 



Formation and locality. — Upper Cambrian, upper part of Ch'au-mi- 

 tien limestone; Pagoda Hill, 1 mile west- southwest of T'ai-an-fu, 

 Shan-tung, China. 



Collected by Eliot Black welder. 



Genus YORKIA Walcott. 

 Yorkia Walcott, 1897, Proc. U. S. Nat. Mus., XIX, p. 714. 

 YORKIA? ORIENTALIS, new species. 



This species is represented by a single small ventral valve, which 

 has the external characteristics of Yorkia wannerl^ of the Lower Cam- 

 brian." The outline of the valve is transversely and broadly oval in 

 outline, exclusive of the apex rising above the posterior margin; the 

 apex gives a subtriangular outline to the valve when looking down 

 upon it; the apex is moderately elevated, and projects over the poste- 

 rior margin; it is perforated b}^ a rather large aperture just above a 

 small false area. 



The surface of the valve is marked by low, rather broad, concentric 

 undulations, a few fine, concentric strife, and a ver}' finely reticulate 

 ornamentation, formed by the crossing of oblique, elevated, curved 

 lines, which form slight!}^ elongate, diamond-shaped pits between them. 

 Shell substance apparently calcareous. Width of ventral valve, 2.5 

 mm.; length, 2 mm. at aperture, 2.25 mm. at apex; elevation, 0.5 to 

 0. 75 mm. 



Ohservations. — As far as may be determined by the exterior of the 

 valve this species is properly referred to Yo7'Ma. The generic refer- 

 ence, however, will remain in doubt until information is available as 



to the characters of the interior of the valve. 



• 



«Proc. U. S. Nat. Mus., XIX, 1897, p. 715, pi. lx, fig. 1. 



