612 CAMBRIAN BRACHIOPODA. 



which is truncated by a circular opening; posterior slope unknown. Surface, as preserved 

 in the arenaceous shale, marked by concentric striae and lines of growth and obscure, very 

 fine, radiating striae. The substance of the shell appears to be corneous, and to make up sev- 

 eral very thin lamellae that combined make a thin shell. 



The generic reference is doubtful, owing to the corneous, shiny character of the shell. 

 This species and Yorkia? washingtonensis Walcott may belong to a new genus or a subgenus 

 of YorJcia. 



The specific name is given in honor of Mr. J. Miquel, of Barroubio, France. 



FoKMATioN AND LOCALITY.— Passage beds between Cambrian and Ordovician, or Lower Ordovician: (342a) 

 Barren quartzitic beds, Coulouma, Department of H^rault, France. 



YORKIA? ORIENT ALIS Walcott. 



Plate LXXXII, figures 3, 3a. 



Torhia? orientalis Walcott, 1906, Proc. U. S. Nat. Mus., vol. 30, pp. 569-570. (Described and discussed as below 

 as a new species.) 



This species is represented by a single small ventral valve, which has the external char- 

 acteristics of Yorkia wanneri Walcott, of the Lower Cambrian. The outline of the valve is 

 transversely and broadly oval in outline exclusive of the apex rising above the posterior mar- 

 gin; the apex gives a subtriangular outline to the valve when looking down upon it; the apex 

 is moderately elevated and projects over the posterior margin; it is perforated by 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 striae, and a very fine reticulate ornamentation formed by the crossing of 

 oblique, elevated, curved lines, which form shghtly elongate diamond-shaped pits between 

 them. Shell substance apparently calcareous. Width of ventral valve, 2.5 mm.; length, 2 

 mm. at aperture, 2.25 at apex; elevation, 0.5 to 0.75 mm. 



Observations. — As far as may be determined by the exterior of the valve, this species is 

 properly referred to YorHa. The generic reference, however, will remain in doubt until 

 information is available as to the characters of the interior of the valve. 



Formation and locality. — Middle Cambrian: (C71) Massive cli£f-forming limestone in the central portion of 

 Kichou formation [Willis and Blackwelder, 1907, pp. 139 and 145 (2d list of fossils)], 4 miles (6.4 km.) south-southwest 

 of Tungyu, Shansi, China. 



Yorkia wanneri Walcott. 



Plate LXXXII, figures 1, la-i. 



Yorhia wanneri Walcott, 1897, Proc. U. S. Nat. Mus., vol. 19, p. 715, PL LX, figs. 1, la-e. (Described and dis- 

 cussed as below as a new species. The specimens represented by figs. 1, la-e are redrawn in this monograph, 

 PL LXXXII, figs, la, Ic, Ig, Ih, and li, respectively; figs, lb and Ic of the original reference (PI. LX) being 

 both drawn from the specimen represented in fig. Ig of PL LXXXII of this monograph.) 



Shell subcircular to suborbicular in outline, moderately convex, with the apices of the 

 valves marginal. Ventral valve highest at the beak, which is truncated by a circular foraminal 

 opening; cardinal slope angular and slightly incurved, so as to form a narrow false area on 

 each side of the slightly convex, rather broad pseudodeltidium. Numerous casts show the 

 pseudodeltidium, false area, and a large filling or cast of the foramen which extended obliquely 

 backward through the thickened umbonal portion of the shell to the apex. On a cast of the 

 interior of the valve tliere are two elongated muscular or vascular (probably the latter) im- 

 pressions that extend from the anterolateral base of the foraminal opening inward nearly to 

 the median line, and then diagonally outward toward the anterior lateral margin of the shell. 

 There is also a slight median longitudinal ridge that corresponds to a depression in the inte- 

 rior of the shell (PI. LXXXII, figs, lb and Ic). In other casts striae or hnes only are shown 



