rORMATIONS AI«rD FOSSILS OF SOUTH MAFCHTJillA 49 



Description. — Shell small, broader than long, subelliptical to 

 quadrilateral, the hinge line about one-half as long as the width of 

 the shell, the cardinal extremities rounded. Pedicle valve moderately- 

 convex on the umbo, with a broad and profound mesial sinus to- 

 ward the front, the surface of the valve anteriorly, which slopes 

 toward the sinus, being about one-third the total width of the shell ; 

 the beak is rather small and slightly incurved. Brachial valve rather 

 convex, most prominent along the median line, mesial fold broad and 

 scarcely differentiated from the lateral slopes; beak small, slightly 

 incurved. 



As is seen in Plate 34, Figures 17 and 18, this species is character- 

 ized by having a spondylium supported by a stout median septum 

 and two smaller lateral septae. 



External surface of both valves ornamented by rather broad, con- 

 centric undulations and very fine radiating striae ; very fine concen- 

 tric striae occur on the interspaces between the raised undulating 

 lines. 



The dimensions of a pedicle valve are: Length, 8 mm; width, 

 about 10 mm. 



Forrrhation and locality. — Ordovician : Near Huang-pa-yi, Shensi, 

 China. 



Gotypes.—J].^:^.^. No. 83644. 



P0LYT0ECHIA7 TAPUENSIS, new species 

 Plate 31, Figttbe 1 



Of this species only a single, somewhat imperfect, pedicle valve 

 is known, which, because it has the characteristic spondylium, may 

 be identified as a member of the genus PolytoecMa. 



Description. — Shell transversely semicircular in outline, wider 

 than long, the hinge line straight, shorter than the width of shell; 

 cardinal angle obtuse. 



The umbonal cavity of this valve is somewhat broken, so that the 

 features can not be clearly seen, but the spondylium appears to be 

 supported by a number of septae, and the umbonal cavity of the valve 

 may be divided into several chambers. 



Valve moderately convex, surface covered with fine radiating 

 striae and unaulating, concentric growth lines, without evidence of 

 a median sinus. 



The dimensions of a single specimen are: Length, about 9 mm; 

 width, 11.5 mm. 



ForTTiation and locality. — Upper Canadian, Santao formation: In 

 the gray banded limestones near Ta-pu, just north of the Pen-hsi-hu 

 colliery, Liao-tung, Manchuria. 



Holotype.—\].^:^M. No. 83645. 



