DESCRIPTION OF GENERA AND SPECIES. 97 



series just above the white quartzite [see Blackwelder, 1907/1, p. 92, for general sec- 

 tion giving stratigraphic relations], collected in a low bluff on the shore of Tschang- 

 hsing-tau Island, east of Niang-niang-kung, Liau-tung, Manchuria, China. 

 Collected by J. P. Iddings and Li San. 



In the argillaceous shales (36g) above the limestones of 35 n and 35 r, a few 

 specimens were collected of a slender, flattened Orthotheca that is probably O. Jclphits. 

 This form I refer to as Orthotheca cf. delphus, as the material is too poorly preserved 

 for an accurate determination of its specific relations. 



Orthotheca doris Walcott. 



Plate 6, Figure 2. 



Orthothcca doris WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 21 . (Described and discussed 

 as a new species essentially as below.) 



Shell elongate, slender, and regularly tapering. Transverse section oval or 

 circular; in the type and only specimen the shell is somewhat crushed, which leaves 

 the original form in doubt. The dorsal face appears to have been moderately 

 convex, with rounded lateral angles that pass into the convex, rounded ventral side. 

 Transverse striae and lines of growth indicate that the aperture was probably trans- 

 verse. Shell apparently strong. 



Surface of shell transversely or concentrically marked by lines of growth, with 

 more or less irregular striae between them ; in addition there is a finely pitted surface 

 between the stria?, and sometimes on them, that gives a very peculiar aspect to the 

 surface under a strong lens. 



The fragment representing this species has a length of 7.5 mm., with a trans- 

 verse diameter at the larger end of 5 mm. 



This species is characterized by the peculiar, irregularly pitted surface. 



Formation and Locality. Middle Cambrian: (C32) A fine-grained bluish-black 

 limestone bowlder believed to have come from the lower part of the Ki-sin-ling 

 limestone [Blackwelder, 19071-, p. 272], collected in river drift i mile (1.6 km.) 

 south of Chon-p'ing-hien, on the Nan-kiang River, southern Shen-si, China. 



Collected by Bailey Willis and Eliot Blackwelder. 



Orthotheca glabra Walcott. 



Plate 5, Figures 23, 230; Plate 6, Figure 7. 



Orthotheca glabra WALCOTT, igii, Smithsonian Misc. Coll., vol. 57, No. 4, pp. 75-76, figs. 5 and 50. 

 (Described and discussed as a new species essentially as below.) 



Form an elongate, slender, rounded tube, with the dorsal face less convex 

 than the sides and ventral face. Transverse section round, except for the slightly 

 flattened dorsal side. Operculum unknown. Shell rather thick, and with a smooth 

 surface. 



The largest specimen in the collection has a length of 5 mm. 



This species is distinguished from other Chinese forms by its rounded tube and 

 smooth surface. It is the representative in form of the American Orthothcca corn- 

 mums Billings. 1 



Orthotheca glabra occurs abundantly in association with Hyolithes cybele Wal- 

 cott, in the Dorypyge richtho/eni zone of Manchuria. Some of the shells have a 

 long, slender, terminal section to the tube that is more or less slightly curved. It 



'Tenth Ann. Rept. U. S. Geol. Survey, 1890, plate 77, figs. 3, j,a-g. 



