(I) 46 



Palxontologia 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. S and 0), taken essentially parallel 



Fig. 6. Chilli iorrras nalhani. Restored longitudinal section, constructed from actual measurements along 

 section a-b and c - d, and tlie 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. cK-final sheath, or endoconic lining; s/i-shcll- 

 wall o{ siphuncle (ectosiphuncle). .sf-stereoplasmic filling of siphuncle; st-endosiphotube; ri-section of rock matrix. 



Fig. 8. 



Fig. 9. 



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

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

 endoconic lining or final sheath; /a-lateral alveolus; ///'(-median alveolus; s/t-shell of siphuncle (ectosiphuncle); .f(-stere- 



op'asmic filling. 



Fig. 8. ChiliUijn-ms nalhani. Somewhat restored section .along line a-h. fig. 6. (For actual appearance of 

 section see Plate II, fig. 11.) -2/3 natural size. Ttie soction is cut obliquely to the axis of the lateral alveoli (see text 

 fig. 2), and cuts the lateral walls (iii) as well a^ the lower walls (inn) of the lateral alveoli; en.s-older endosheaths buried 

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



Fig. 9. Chihlioceras nathani. 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. <S 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. -1 and 5. The walls, 



