DESCRIPTION OF GENERA AND SPECIES. 83 
This species is distinguished from all other species by the strong, incurved 
umbo, and rounded ribs with narrow interspaces. 
Formation and Locality—Middle Cambrian: (C75) Limestone near the base 
of the Ki-chéu formation [Willis and Blackwelder, 1907, p. 143], 4.5 miles (7.2 km.) 
south of Wu-t’ai-hién, Shan-si, China. 
Collected by Eliot Blackwelder. 
Eoorthis linnarssoni (Kayser). 
Plate 4, Figures 11, 114. 
Orthis linnarssoni KAYSER, 1883, China, Richthofen, vol. rv, p. 34, plate m1, fig. 1. (Described and 
discussed in German as a new species; see below for translation. Fig. 1 is reproduced by Walcott, 
1giI, plate xcvil, fig. 5a.) 
Orthis (Plectorthis) linnarssoni (Kayser), WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvii, p. 266. 
(Original description copied and species discussed as below.) 
Eoorthis linnarssoni (Kayser), WALCOTT, 1912, Monogr. U.S. Geol. Survey, vol. Li, pp. 782-783, plate 
xcvil, figs. 5, 5a. (Copy of the preceding reference.) 
The original description by Kayser follows: 
“Shell semielliptical in outline, broader than long, with hinge edge straight, 
corresponding to the greatest breadth of the shell. Large (ventral) valve moder- 
ately convex. Small (dorsal) valve slightly arched, with a sinus which develops 
at the umbo, and grows quite broad and deep toward the edge. Umbo of ventral 
valve small, area very low. Surface of shell covered with rather sharp ribs, exceed- 
ingly variable in strength, separated by narrow furrows. By reason of repeated 
splitting, which begins close to the umbo, the ribs appear more like bundles of ribs. 
On the matrix these bundles appear as broad, obtuse-angled folds, which, owing to 
repeated marginal splitting in even a higher degree than on the shell itself, appear 
as bundles of ribs of very unlike strength. When the surface is well preserved, a 
delicate concentric growth striation is perceptible.” 
Doctor Kayser compares this shell with Billingsella hicksi (Salter) [Walcott, 
1912b, plate xcvui, figs. 7, 7a—b] and Billingsella exporrecta (Linnarsson) [idem, plate 
LXXXvIitl, figs. 1, ra—l], on account of the surface characters. It does not appear 
to be very closely related to either species, but it is in many respects allied to 
Eoorthis desmopleura (Meek) [idem, plate xcv1, figs. 1, 1ta—-r] and E. wichitaensis 
(Walcott) [idem, plate xcrv, figs.1,1a-o,1u]. Eoorthis linnarssoni differs from both 
in being more transverse. This species is represented by a dorsal valve, illustrated 
by figure 11, from near Yen-chuang. 
Formation and Locality—Upper Cambrian: (C64) Upper limestone member 
of the Kiu-lung group [Blackwelder, 1907a, pp. 37 and 42 (first list of fossils), and 
fig. 10 (bed 20), p. 38], 2.7 miles (4.3 km.) southwest of Yen-chuang, Sin-t’ai district, 
Shan-tung, China. 
Another dorsal valve that is very closely related to, if not identical with this 
species, occurs in stream gravels at Locality C67, Upper Cambrian: stream gravels 
(these are taken from the wash from the mountains south of the city) used in making 
the railroad grade one-third mile (0.5 km.) west of the west city gate at Tsi-nan, 
Shan-tung, China. 
Collected by Eliot Blackwelder. 
Eoorthis pagoda (Walcott). 
Plate 4, Figures 12, 12a-d. 
Orthis (Plectorthis) pagoda WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvii, pp. 267-268. (Described 
and discussed as on page 84 as a new species.) 
Eoorthis pagoda (WaLcort), 1912, Monogr. U.S. Geol. Survey, vol. LI, pp. 784-785, plate xcvu, figs. 
12, 12a-d. (Copy of the preceding reference.) 
