DESCRIPTION OF GENERA AND SPECIES. 95 



and without any ventral angle. Aperture, as far as known, transverse, at right 

 angles to the axis of the shell. Operculum unknown. Shell of moderate thickness 

 and made up apparently of several layers or lamella?. 



Surface of the shell concentrically or transversely finely striated ; a few longi- 

 tudinal striae may be seen by turning the specimen in the light. 



The largest specimen, which is broken off at the apical end, has a length of 

 9 mm., with a width on the dorsal side at the larger end of 2 mm. ; a specimen with a 

 diameter of 3 mm. on the dorsal face has a dorso-ventral diameter of 2 mm. 



What appears to be a transverse septum occurs in one of the shells about 9 mm. 

 from the apical end. 



The elongate form of the tube and the shallow groove on the center of the 

 dorsal face are notun^keOrthothecacommunisemmonsi^Pofd} [Walcott, i89ia,p.62i, 

 plate 77, fig. 46]. The two species, however, differ in the outline of the transverse 

 section and in the more rapidly expanding tube of Orthotheca cyrene. There are 

 a number of species from the Swedish Cambrian, illustrated by Holm, that have the 

 central depression on the dorsal face. Of these, Orthotheca affinis Holm [1893, P- 

 60, plate i, figs. 57-69; plate 5, figs. 59-63; plate 6, fig. n] is most nearly related 

 to O. cyrene. 



Formation and Locality. Upper Cambrian: (C47) Upper part of the Ch'au- 

 mi-tien limestone [Blackwelder, 19070, fig. 9 (top of bed i), p. 35], at the top of 

 a high col at Ch'au-mi-tien, Shan-tung, and (C64) upper limestone member of the 

 Kiu-lung group [idem, 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. 



Collected by Eliot Blackwelder. 



Two specimens of this species occur in limestone of the Dorypyge richthofeni 

 zone in Manchuria. 



Formation and Locality. Middle Cambrian: (35 n) Fu-chou series; limestones 

 near the base of the series just above the white quartzite [see Blackwelder, 19076, 

 p. 92, for general section 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. 



Orthotheca cyrene dryas Walcott. 

 Plate 5, Figures 22, na-c. 



Orthotheca cyrene dryas WALCOTT, 1905, Proc. U. S.Nat. Mus., vol. xxix, p. 19. (Characterized as a 

 new variety as below.) 



This variety is characterized by having a broader, more shallow furrow on the 

 dorsal face; otherwise it appears to be identical with 0. cyrene [p. 94]. On some 

 specimens the shallow groove is scarcely perceptible, the face being practically 

 transverse and smooth. 



Formation and Locality. Middle Cambrian: (02) Lower shale member of 

 the Kiu-lung group [Blackwelder, 19070, pp. 37 and 40 (part of the third list of 

 fossils), and fig. to (beds 4 and 5), p. 38], 2 miles (3.2 km.) south of Yen-chuang, 

 Sin-t'ai district, Shan-tung, China. 



Collected by Eliot Backwelder. 



Orthotheca daulis Walcott. 



Plate 5, Figure 24. 



Orthotheca daulis WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 20. (Described and discussed as 

 a new species essentially as on page 96.) 



