Scientia Sinica

158 SCIENTIA SINICA Vol. V

Discussion: There are no Paleobolus known in China. This new species distinguishes itself from Pal@obolus bretonensis (Matthew)") by its small size and by the closeness of the surface ridges.

Paleobolus rotulus Wang (sp. nov.) (Pl. 1, B; Fig. 1) Represented by a single ventral valve.

Size small; general form broadly ovate; lateral margins gradually acuminate toward the posterior end; anterior margin rounded; lateral profile evenly and moderately convex. Surface marked by fine, elevated concentric lines.

_ Dimensions (mm): Length 5.2; width 5.4. Figured specimen, I.P.A.S. 7982.

Horizon and Locality: Kushan Formation, Upper Cambrian; summit of Nanchimao Hill, Pangchiawa, southwest of Chiawang Colliery, Kiangsu Province.

Collector: J. C. Sheng.

Discussion: This species differs from Paleobolus discus (sp. nov.) in its smaller size and in its more delicate ornamentations.

Genus Westonia Walcott 1901 Westonia obovata Wang (sp. nov.) (PL. 1, C; Figs. 1-2) Represented by several ventral valves.

General outline subrounded, greatest width near the anterior margin; posterior extremity gradually acuminate, anterior margin broadly rounded; evenly and gently convex in lateral profile, with the greatest convexity about at the middle of the valve. Surface marked by fine concentric growth lamellae; semi-imbricate, ripply lines well developed in whole surface.

Dimensions (mm): Length 11.7; width 11.2. Figured specimens, I.P.A.S. 7983, 7984.

Horizon and locality: Kushan Formation, Upper Cambrian; limestone quarry near Changshan, Chiawang Coal Field, Kiangsu Province.

Collector: J. C. Sheng.

Discussion: his species differs from the hitherto known members of the genus Westomia by its subrounded outline and by its greatest width of the valve near the anterior margin.