DESCRIPTION OF GENERA AND SPECIES. 91 



the end of 4 by 5 mm. The largest diameter at the aperture was probably about 

 10 mm. 



The generic reference of this specimen is doubtful, but in the absence of the 

 outer shell it is not possible to determine the generic relations. 



Formation and Locality. Upper Cambrian : (046) Light gray, crystalline lime- 

 stone on the Ch'ang-hia limestone [Blackwelder, 19070, p. 33 (fourth list of fossils)], 

 at Ch'au-mi-tien, Shan-tung, China. 



Collected by Eliot Blackwelder. 



Helcionella rugosa chinensis (Walcott). 



Plate 5, Figure 8. 



Stenotheca ni^osa cJiinensis WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 16. (Described and 

 discussed as a new species essentially as below.) 



In its general form this shell is closely related to Helcionella rugosa; it is, 

 however, more elevated and more broadly oval in outline than the typical forms 

 of H. rugosa. The surface is marked by a number of moderate undulations, or low, 

 concentric ridges, and numerous very fine, concentric striae of growth; with a strong 

 lens fine radiating striae are visible. 



The type and only specimen in the collection has a longer diameter at the aper- 

 ture of about 10 mm., with a height of 7 mm. to where the apex is decorticated; at 

 this point the oval section has a length of 2.5 mm., with a width of 1.5 mm. The 

 apex is broken off at a smooth, slightly convex septum. 



This specimen is of unusual interest, owing to the presence of a septum toward 

 the apex. In form it resembles most closely H. rugosa acutacosta (Walcott) [18910, p. 

 617, plate 74, figs. 2, 2ab], but differs from that variety in the presence of rounded 

 instead of acute costae. From H. rugosa it differs in being elevated and more or 

 less conical. 



Formation and Locality. Lower Cambrian: (Co) Lower part of the Man-t'o 

 shale formation [Blackwelder, 19070, p. 28 (list of fossils at bottom of page), and 

 fig. Sa (bed 20), p. 28], on the southeast slope of Hu-lu-shan, 2.5 miles (4 km.) 

 southwest of Yen-chuang, Sin-t'ai district, Shan-tung, China. 



Collected by Eliot Blackwelder. 



Helcionella rugosa orientalis (Walcott). 



Plate 5, Figures 15, 153. 



Stenotheca rngosa orientalis WALCOTT, 190.5, Proc. U. S. Nat. Mus., vol. xxix, p. 16. (Described and 

 discussed as a new species essentially as below.) 



This variety is founded upon a small, slender shell with a rounded, oval aper- 

 ture. In form it is between Helcionella rugosa acutacosta (Walcott) [18910, p. 617, 

 plate 74, figs. 2, 2a-b] and H. rugosa crccta Walcott [idem, fig. 4], being slender, 

 slightly arched, and cornucopia-like. Surface marked by strong, sharply angular, 

 concentric ridges, with broader U-shaped furrows between them, and numerous fine 

 concentric striae. The average length of the shells of this species is 3 mm., with a 

 diameter at the aperture of 1.5 to 1.75 mm. 



Formation and Locality. Middle Cambrian: (C21) Ocher-mottled phase of 

 purple-gray limestone in the middle of the oolitic Ch'ang-hia formation [Blackwelder, 

 19070, p. 33 (second list of fossils)], at Ch'ang-hia, and (CIS) dark gray oolitic 

 limestone about 400 feet (120 m.) above the base of the Ch'ang-hia limestone [idem 

 (third list of fossils)], in cliffs i mile (1.6 km.) east of Ch'ang-hia, Shan-tung, China. 



Collected bv Eliot Blackwelder. 



