(iv) 18 Palxontologm Sinica Ser. B. 



Shell small, of subovate outline; moderately convex, length and width subequal. 

 Posterior border nearly straight meeting at the beak and forming an obtuse angle 

 (110°). Anterior lateral borders rounded, frontal margin more gently rounded. Con- 

 vexity most pronounced near the umbonal region, the shell becoming flattened towards 

 the front. 



Surface uneven, marked by fine irregular, concentric line of growth, and a few 

 coarse concentric wrinkles. 



This shell shows almost exactly the characters . of the species described under 

 Obolus mollisonensis by Walcott from the Lower Ordovician of Mount Mollison British 

 Columbia, and although the interior characters are not known, I tentatively refer it to 

 that species because of the agreement in form. 



This shell also resembles Obolus (Broggeria) salteri (Holl) of the Upper Cam- 

 brian and Lower Ordovician of north western Europe, but the surface features of Obolus 

 {Brdggeria) salteri are absent in our specimens; and the agreement is closer with the 

 Mount Mollison specimen. Only two specimens of this species have been found in China, 

 one of which is poorly preserved. 



A comparison of the measurement of our best specimen (Fig. 4 a) and of W- 

 American and European forms give as follows; 



Walcott type 

 5.3 mm. 



5.0 mm. 



0. (Broggeria) salteri 



6.0 mm. 



0.8 mm. 



Horizon AND Locality : — Early Upper Cambrian : from purple shale of Chang- 

 shan formation of Chao-kou-chuang, Luan-Hsien, Chihli: collected by Survey Expedition. 



Obolus linyuensis Sim (sp. nov.) 



Plate I. Fif^. 5. 



Shell small, oval; modeiately convex, length slightly greater than the greatest 

 width. Posterior borders nearly straight meeting at the beak approximately in an angle 

 of 80°. Antero-lateral borders rounded. 



Surface marked by lines of gi-owth which are regular, giving a smooth and glis- 

 tering appearance, l^ut becoming more coarse in the anterior part. 



This species is represented by only one specimeia and characterized by its sinall 

 glistening shell with concentric lines of growth regularly arranged. 



