(i) 76 Palasontologia Sinica <Ser. B 



only at the rate of 1 in 6 or 7 dorso-ventrally. Shell-surface apparently with longitudinal 

 fiexuous strife; sutures somewhat flexuous, slightly arching forward on one of the sides. 

 Average distance between cameras 3.75 mrn., less in the younger stages. Depth of 

 cameras, in center, equal to about 3 camera-lengths or slightly more. Siphuncle nummu- 

 loidal, large, centran, and oval in section, corresponding to the section of the shell. It 

 increases less rapidly in diameter than does the shell, its lateral diameter being 14 mm. 

 where that of the shell is 41 mm., (Plate IX, fig. 7) ; and 10 mm. where that of the shell 

 is 30 mm. while its dorso-ventral diameter is 11.5 mm. where that of the shell is 28 

 mm., and 9 mm. in the younger stage, where that of the shell is only 24 mm. (Plate IX, 

 fig. 8). It is thus more nearly circular in section in the younger stages. Siphuncle as a 

 rule only partially filled by rosettes of stereoplasm, leaving a large central tube, from 

 which lateral, more or less forward-bending diverticula extend into the nummuli.* 

 Cameras only partially (seldom entirely) filled with secondary stereoplasm. 



The most complete specimen obtained is a fragment of the lower part of a large 

 conch preserving 12 cameras complete and portions of 3 others. This specimen is shown 

 on Plate IX, figs. 7a-7e, and clearly shows the oval section which in the upper part is 41 

 mm. in lateral, and 27 mm. in dorso-ventral diameter. Three views of the specimen were 

 drawn (7a-7c), after which it was sectioned, the two sections being shown in figs. 7d-7e. 

 The form of the eiphuncle corresponds to that of the shell, and its two diameters at the 

 upper end of the fragment are each about one third that of the corresponding diameter of 

 the shell. The nummuli are only partially filled with rosettes of stereoplasm, leaving a 

 large median tube from 2 to 2.5 mm. in diameter. At the lower end of the specimen the 

 diameter of the lower nummulus is 11.5 mm., the form being practically circular. At the 

 upper end, the nummulus, next to the highest complete nummulus, has a diameter of 

 15.3 mm. while the highest completely preserved one, has a diameter of only 14mm. 

 Here the dorso-ventral diameter is also 11.5 mm. This shows that while there is in 

 general an increase in diameter laterally, there is also some variation. From the median 

 tube, a lateral tube traverses the center of each nummulus, in some cases extending 

 outward approximately at a right angle, in others bending slightly forward. Again it may 

 bend forward and then outward as seen in the second nummulus from the top (fig. 7e). 

 In a few cases the opening of this tube in a pore on the periphery of the nummulus is 

 well shown in the sections. 



The septa are thickened by secondary stereoplasm, which appears to occur both 

 on the upper and under side of the septum, though this feature is somewhat obscured by 



* The term nummulus (pi. nummuli) is here used for the individual beads of the nnmmuloidal siphunclr. 

 whether these are tilled with secondary deposits or empty. These nummuli may be compared to the individual checker- 

 like elements dm (|^) of the Chinese calculating frame or Suanjj'an 



