(i) 46 



Palseontologia Sinica 



Ser. B 



final endosheath is nearer the dorsal than the ventral side of the siphuncle (text fig. 6) 

 as is shown by the two parallel sections (text figs. 8 and 9), taken essentially parallel 



x 



t 



i 



e.. 





si 



Fig. 6. Chihliof.eras nathani. Restored longitudinal section, constructed from actual measurements along 

 section a-b and c- d, and the exposed worn surface of the ventral side (lower dotted line), and with the aid of other 

 specimens, x - y line of section shown in fig. 7. Two thirds natural size. en-final sheath, or endoconic lining; gft-shcll- 

 wall of siphuncle (ectosiphuncle). s<-stereoplasinic filling of siphuncle; sj'-endosiphotube ; rfc-section of rock matrix. 



y/m 



:-.-ens 



Fig. 8. 



Fig. 9. 



Fig. 7. Chihlioceran nathani. Transverse section along line x - y of fig. 6; 2/3 natural size, e - f. line of 

 section of fig. 10; g - h. line of section of fig. 11 ; i - j. line of section of fig. 12; k - 1. line of section of fig. 13; en-parts of 

 endoconic lining or final sheath; Za-lateral alveolus; Wia-median alveolus; sft-shell of siphuncle (ectosiphuncle); sZ-stere- 

 op'asmic filling. 



Fig. 8. Chihlioceras nathani. Somewhat restored section along line a-b. fig. 6. (For actual appearance of 

 section see Plate II, fig. 11.) -2/3 natural size. The spction is cut oblique'y to the axis of the lateral alveoli (see text 

 fig. 2), and cuts the lateral walls (wl) as well as the lower walls (wm} of the lateral alveoli; ens-older endosheaths buried 

 in the filling of stereoplasm st. (Other notations as in figs. 6 and 7.) 2/3 natural size. 



Fig. 9. Chihlioceras nat-hani. Corresponding restored section along the line c - d in fig. 6. This section is 

 here reversed, so that the parts have the same orientation as in fig. 8. Notation as in fig. 8. 2/3 natural size (See Plate 

 IT, fig. 12). 



to the ventral surface of the siphuncle, as indicated by the lines a-b and c-d in text fig. 6, 

 which is drawn to scale, and is two thirds natural size. The sections (text figs. 8 and 

 9) show that the walls of the alveolar cavities are infolded portions of the. sheath, which, 

 when considered separately i. e. as if freed from the enclosing organic lime - deposit, 

 represents the aspect shown by the model, illustrated in text figs. 4 and 5. The walls, 



