Vol I. Grabau Ordovician Fossils from North China (i) 69 



Another specimen from Lincheng Shantung, referred to this species, has a septal 

 distance of 7 mm. where the shell is 21 mm. in diameter. The rate of tapering of this 

 specimen, as indicated in the section, is 1 in 8.5. There is comparatively little stereo- 

 plasm in the camerse, and it appears to be confined to the upper surface of the septum 

 and bounded above by a pseudoseptum. The siphuncle is not shown in this specimen. 



This species differs from S. pseudoseptatum in its proportionately more distant 

 and somewhat shallower septa, in the narrowly nummuloidal siphuncle, the comparative- 

 ly few pseudosepta and the frequent complete filling of the camerse with stereoplasm. 



HORIZON AND LOCALITIES: In the Machiakou limestone at Machiakou Chihli 

 province, (H. C. T'an, cat. no. 15,) and in the same horizon at Lincheng, Shantung 

 province (F. F. Mathieu, cat. no. 79). In both places the species is associated with 

 Actinoceras richthofeni, A tani etc. and is of early Upper Ordovician age. A specimen 

 referred with some hesitation to this species, because of its narrower septal interval (4 

 where the diameter is 14 mm., 4.5 where it is 18 mm.) came from Tse-yan, Ning-yang 

 Hsien, Shantung. It has the same rate of tapering, and slight amount of stereoplasm 

 found in the Lincheng specimen. (Survey collection cat. no. 82). 



Stereoplasmoceras actinoceriforme Grabau (sp. nov.) 

 Plate IX, figs. 9a-b, lOa, b. 



Shell rather strongly tapering, the rate varying from about 1 in 6, to 1 in 7, with 

 the cross-section either subcircular to suboval, and the siphuncle nearly centran, or 

 circular with the siphuncle slightly excentric. The dimensions of the lower end of a 

 well-preserved section (Plate IX, fig. 9b) are: transvese diameter, 17 mm., distance from 

 center of siphuncle to ventral (?) side, 7 mm.. 



Siphuncle strongly nummuloidal, giving the shell an Actinoceras-like appearance, 

 but without the regular siphonal fillings characteristic of that genus. In one specimen 

 (Plate IX, fig. lOa) the siphuncle appears to have been wholly empty, becoming filled 

 with the fine matrix of calcilutyte, in which the shell was embedded. This, in the lower 

 two nummuli preserved, has separated out, showing the inside of the wall of the 

 nummulus which is quite regular and fairly smooth. In a second, larger, specimen 

 (Plate IX, fig. 9a, b) the nummuli are filled with coarsely crystallized calcite, the 

 outlines of which are distinct from the walls of the nummuli. 



