( I ) 68 Palseontologia Sinica Ser. B 



section, and 5 mm., where the section is 18 mm. wide. The septal interval ranges from 

 about 3.8 mm. in the lower, to 4 mm. in the upper part. The concavity of the septa is 

 equal to nearly 2 camera lengths. In the median portion of the specimen, the nummuli 

 show a distinct narrow central tube, which extends from septum to septum. Around 

 these septal necks, there is an irregular deposit of stereoplasm which partly fills the 

 nummuli, the remainder being filled by crystalline calcite of secondary origin. The 

 central tubes or septal necks, stop abruptly at a septum about one-third the length of the 

 fragment from the bottom, this abrupt cessation suggesting that they are not present in 

 the earlier nummuli, which contain only an irregular deposit of stereoplasm. The 

 pseudosepta are of the type described for the larger specimens of this species. 



HORIZON AND LOCALITIES: So far as known, this species is confined to the 

 Machiakou limestone where it is associated with Actinoceras. Characteristic specimens 

 have been obtained from Lincheng in Shantung (F. J\ Mathieu), from Ningyang, 

 Shantung, and Tangshan and Lushan, Chihli, (Survey collection), from Wen-nan, 

 Mon T Yin-Hsien Shantung (V. K. Ting coll.) and from Chaokouchuang, Chihli (Survey 

 expedition of 1921). It is thus seen to be a widespread species. 



Stereoplasmoceras machiakounense Grabau (sp. nov.) 



Plate VI, Figs. 8 



Shell subcylindrical, tapering very gently, section apparently circular, siphuncle 

 subcentran. 



Septa moderately concave, the depth equal to about one camera. Septal distance 

 varying from 4 mm. in the lower part of the fragment, to 6 mm. in the upper, the 

 diameter of the shell being about 20 and 21 mm. respectively. Pseudosepta irregularly 

 developed, occurring in one part of a chamber but absent in another. Some cameras are 

 without pseudosepta, and are solidly filled with stereoplasm. In other cases, the camera 

 on one side of the section is without stereoplasm, while on the other side, where a 

 pseudoseptum is present, it may be partly filled by this deposit. So far as can be 

 ascertained the stereoplasm is confined to the upper surface of the septum. 



Siphuncle gently nummuloidal the nummuli swelling to a diameter of 5.3 mm. 

 in the center, and contracting to 3 mm. at the septal ends. There is no stereoplasm in 

 the siphuncle which is filled only with the matrix. 



