(]) 70 Palseontologia Sinica Ser. B 



Diameter of nummuli varying from 5 to 5.5 mm. and their length, which is also 

 the septal interval, from 2.7 mm., where the diameter of the shell is from 1ft to 18 mm. 

 (Plate IX, fig. lOa), to 3 mm. or a little over, where the diameter is 20 mrn. (Plate IX, 

 fig. 9a). Depth of septa a little more than one camera length. Pseudosepta and stereo- 

 plasmic deposits in the camerte very irregular. * 



This species differs from the others of this genus in its suboval section, nearly 

 centran siphuncle, and short septal interval, as well as in its irregular pseudosepta and 

 stereoplasmic deposits. From S. machiakounense it differs, moreover, in the strongly 

 nummuloidal siphuncle, the nummuli of which are much broader than long, whereas it is 

 the reverse in S. machiakounense. From S. pseudoseptatum it differs in its smaller size, in 

 the subcentran position of the siphuncle, and in the irregularity of the pseudosepta and 

 stereoplasm; also in the regularity of the siphonal nummuli, and their complete freedom 

 from deposits of stereoplasm. The species might easily be mistaken for an Actinoceras, 

 but the absence of annular deposits shows that it belongs to the Loxoceratidie. 



HORIZON AND LOCALITIES: In the Machiakou limestone of early Upper Ordovician 

 (Black River) age at Kushan, Chihli, and at Wen-nan Mon-Yin-Hsien Shantung (V. 

 K. Ting coll.). 



Family ACTINOCERATID^E Samann, 



Genus ACTINOCERAS Bronn 



The type of this genus is Actinoceras bigsbiji Bronn, a widely distributed 

 American species, which occurs in the late Middle and early Upper Ordovician (Stones 

 River, Black River and Trenton). It ranges from Tennessee northward to arctic America 

 (Iglook Island, Fox Channel), westward to Iowa and Lake Winnipeg, and eastward to 

 New York. The shell expands rapidly at first forming an irregularly conical apical end 

 which is characterized by a large foramen, surrounded by a distinctly swollen ring. 

 This feature has been figured by Foord for A. bigsbyi from arctic America and Canada, 

 and it is equally well shown in a specimen of A. tani in the survey collection (Plate 

 VII, figs. 7a, b). The apical cone of Actinoceras, in the specimens figured by Foord, 

 and in our form, is somewhat asymmetrical. In the American form the apical foramen or 

 scar is moreover situated obliquely, while in the Chinese form it is normal to the axis. 

 This foramen apparently marks the point of decortication of the embryonic chamber or 

 protoconch. 



