BILLINGSELLID^. 793 



Pompeckj [1896b, p. 514] mentions another species of Orthis that appears to belong to the 

 genus Eoortliis. The material, which is too imperfect for specific determination, was described 

 as follows : 



The impression of a dorsal valve departs from Orthis romingeri in its greater breadth and less distinct ribbing. 



Formation and locality. — Middle Cambrian: (345e [Pompeckj, 1896b, p. 514]) Greenish shale in the Paradoxides 

 zone in the gorge above Luh, near Skrej, Bohemia, Austria-Hungary. 



EooRTHis sp. undt. c (Walcott). 



Plate LXXXIX, figure 7. 



Orthis (Plectorthis) sp. undt. Walcott, 1906, Proc. U. S. Nat. Mus., vol. 30, p. 571. (These various shells are described 

 and discussed essentially as below as sp. undt. c, d, and e.) 



This species is represented by a single specimen of the ventral valve. Ventral valve 

 convex, with the apex curving gently downward from the liighest 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 slightly forward from the liinge hue. 



Surface marked by about 16 strong, nearly regular, rounded, radiating ribs, that are 

 crossed by fine, concentric striae, lines of growth, and one strong ridge indicating interruption 

 of growth. 



Oiservations. — Tliis little shell was at first placed with Eoorthis agreste (Walcott) (PI. 

 LXXXIX, fig. 6), but fui'ther study showed that its greatest convexity, elevated apex, and 

 stronger ribs distinguished it from that species. 



FoKMATiON AND LOCALITY. — Middle Cambrian: (C26) Near the top of the black oolite group in the uppermost 

 layers of the Changhia formation [Blackwelder, 1907a, p. 33 (part of the last list of fossils)]; 2 miles (8.2 km.) north- 

 northeast of Changhia, Shantung, China. 



^. EooETHis sp. undt. d (Walcott)." 



Plate LXXXIX, figure 8. 



A larger shell of the type of sp. undt. c occurs in Shensi, in the central portion of the 

 Kichou formation. It has a length of 6.5 mm. and a mdth of 7.5 mm. The surface is 

 naarked by numerous radiating ribs, similar to those of the shell from Changhia, also concen- 

 tric strise and several ridges resulting from interruption of growth. 



Formation and locality. — Middle Cambrian: (C71) Massive cliff-making limestones in the central portion of 

 the Kichou formation [Willis and Blackwelder, 1907, pp. 139 and 145 (2d list of fossils)], 4 miles (6.4 km.) south- 

 southwest of Tungyu, Shansi, China. 



Eoorthis sp. undt. e (Walcott)." 



A tliird shell that appears to be a dorsal valve was found associated with Middle Cambrian 

 trilobite fragments in limestone pebbles in river gravel. The surface is partly exfoliated, 

 but it shows rounded, radiating ribs and concentric ridges, similar to those on the two specimens 

 described above as sp. undt. c and sp. undt. d. 



Formation and locality. — Upper Cambrian : (C67) Stream gravels used in making the railroad grade, 0.33 mile 

 (0.5 km.) west of the west city gate, Tsinan, Shantung, China. 



Genus FINKELNBTJBG-IA Walcott. 



Orthis {Finhelnhurgia) Walcott, 1905, Proc. U. S. Nat, Mus., vol. 28, pp. 277-278. (Characterized and discussed as 



below as a new subgenus.) 

 Finkelnburgia Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 148. (Classification 



of genus.) 



This genus is based upon two species that differ from Eoorthis in having tliick shells and 

 strongly marked vascular trunks in the ventral valve. The type of the genus, Finkelnburgia 

 jinkelnburgi. with its acuminate and sometimes alate cardinal extremities and subequally convex 



a See synonymy for Eoorthis sp. undt. c. 



