CA MBRIA N FA UXAS OF CHINA— WALCO TT. 571 



ORTHIS (PLECTORTHIS), species undetermined. 



This species is represented by a sino-Ie .specimen of the ventral valve. 

 Ventral valve convex, with the apex curving- gently downward from 

 the highest point to the cardinal area; transverse; length, 2.5 mm.; 

 width, 3 mm.; hinge line a little shorter than the greatest width; 

 cardinal area sloping slightl}' backward from the hinge line. 



Surface marked by about 16 strong, nearly regular, rounded, radi- 

 ating ribs, that are crossed by tine, concentric stria?, lines of growth, 

 and one strong ridge indicating interruption of growth. 



Ohservatioiu. — This little shell was at first placed with Orthis {Plec- 

 tm'this) agreste (p. 570), but further stud}^ showed that its greater con- 

 vexity, elevated apex, and stronger ribs distinguished it from that 

 species, 



ForriKAtion andlocal'dy . — Middle Cambrian, upper portion of Ch'ang- 

 hia formation, near top of dark, oolitic limestone series; 2 miles north- 

 northeast of Ch^ang-hia, Shan-tung, China. 



A larger shell of this type occurs in Shen-si, in the. central portion 

 of the Ki-chou formation. It has a length of 6.5 mm., and a width of 

 7.5 mm. The surface is marked by numerous radiating ribs, similar 

 to those of the shell from Ch'ang-hia, also concentric stria? and several 

 ridges resulting from interruption of growth. 



The locality is 4 miles south-southwest of Tung-yii-chon, Shen-si, 

 China. 



A third shell, that appears to l)e a dorsal valve, was found in lime- 

 stone pebbles in river gravel. The surface is partially exfoliated, but 

 it shows rounded, radiating ribs and concentric ridges, similar to those 

 on the two specimens described above. 



The associated fragments of trilobites suggest the Middle Caml)rian 

 fauna. 



The locality is in the railroad grade, one-third mile west of west 

 city gate, T'ai-an-fu, Shan-tung, China. 



Collected by Eliot Blackwelder. 



GASTROPODA. 



Genus SCENELLA Billings. 

 SCENELLAf DILATATUS, new species. 



This species is based upon two specimens which preserve the expanded 

 outer margin, but not the elevated, central, conical portion of the shell. 

 The exterior outline is oval, the length of the type specimen being 9 

 mm.; width, 7 mm. The surface on the inner side of the campanulate 

 margin is marked by numerous radiating, elevated stria?. As viewed 

 from the lower side the margin slopes gentlv inward to a shallow 

 depression, or furrow, within which there is a rounded, slightly ele 



