FORMATIONS AND FOSSILS OF SOUTH MANCHURIA 47 



radius is intercalated. These principal striations are not so distinct 

 near the cardinal angles. The interspaces between principal stria- 

 tions are crossed by wavelike wrinkles, the crests about as wide as the 

 troughs. There are about 20 crests in 5 mm on the anterior part 

 of the shell. Each wave is steeper on the front than on the back 

 slope. A wrinkle sometimes includes two adjacent interspaces be- 

 tween the ribs but usually alternate so that one interspace is a crest, 

 while the next is the trough of the wrinkle. Near the cardinal 

 angles, each wrinkle is more apt to involve several interspaces. 



The pedicle valve is very convex on the umbo, becoming flattened 

 toward the anterior margin or sometimes slightly concave near the 

 front. Brachial valve flat, beak of both valves inconspicuous. In- 

 terior of valves unknown. 



Average length, 11 mm ; average width at hinge line, 15 mm. 



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

 China. 



Holotype and paratypes. — U.S.N.M. No. 83641. 



Genus CLITAMBONITES Pander, 1830 



CLITAMBONITES HEMISTRIATUS, new species 



Plate 35, Fighbes 7-12 ; Plate 36, Figure 1 



Description. — Shell semicircular ; hinge line straight, almost equal 

 to maximum width of shell; cardinal angles usually right angles. 

 Pedicle valve moderately elevated at the beak, the surface sloping 

 from the umbo to the anterior and antero-lateral margins with a 

 slightly convex curve, sometimes becoming a little concave as it 

 approaches the anterior margin ; the slope to the cardinal extremities 

 somewhat more abrupt; hinge area moderately large and triangular 

 with a comparatively large triangular delthyrium. Brachial valve 

 moderately convex; beak small, inconspicuous, not elevated; hinge 

 area very narrow. 



Ornamentation of valves is very characteristic; outer surface of 

 each valve marked by many fine radiating costae, five or six of which 

 occupy the space of 1 mm ; inner surface of both valves, on the con- 

 trary, marked with comparatively lesser, fine straight primary radii, 

 equidistant and of equal strength, separated by rather wide inter- 

 spaces. These primary striations are separated by interspaces 0.5 

 mm to 1 mm wide, which are occupied by a number of minute, but 

 very fine, longitudinal striations. 



The dimensions of a pedicle valve are: Length, 12 mm; width, 

 14 mm. The dimensions of a brachial valve are : Length, 10.5 mm ; 

 width, 13.5 mm. 



C omparison. — In its general outline this shell may be compared to 

 Clitamihonites chinensis Weller from the Ki-sin-ling limestone, Sze- 



