(I) 



Palaeoiitologia Sinica 



Ser. B 



i-oiimled forward end, and increasing in thickness apicad. (See section, text figures 15 and 

 16). It consists of the thin endoconic ^\alls (reduphcations of the endosheath) and tlie 

 fiUing of crystalline calcium carbonate l)et\veen these. 



Fig. 14. riiihlioceras chinrjiivtigtanciif:,'. Diagrammatic longitudinal section along the median dorso-ventral 

 plane of a restored individual; w-o. -section line of lig. 15; '^-;;. -section line of fig. 16; s/i.-sliell (ectosiphuncular wall;; st. 

 stereoplasmic filling; s/.-endosiphotube; <■//. -endoconic lining or terminal endosheath; fin. -dorsal alveolus; nw. -median 

 alveolus. 



The lateral alveoli are lenticular in section, only the inner, gently concave wall 

 being formed hy a part of the endosheath, while the outer is formed by the wall of the 

 sii)huncle, and in the type sjiecimen, as preserved, is broken away. In this specimen the 



size and form of the tv.o lateral alveoli differ from each other, 

 that on the right * being much larger. The hne of junction 

 between it and the siphuncular wall (shell) is a direct con- 

 tinuation of the plane of the anterior endoconic blade. The 

 sides of this alveolus converge regularly. The left lateral 

 alveolus is more irregular. At fii-st there is a strong conver- 

 gence of the sides, after which they continue more nearly 

 parallel. Posteriorly tlie two alveoli join into a single broad 

 section along line m-n. in fig. 14; median cavity, the floor of which is formed bv the two lateral 



7-r, -median d(jrso- ventral plane 



(line of section of tig. 14); s-«. -line alvcolar floors meeting in a low angle, to the left of the 



of section of fig. 16: Za.-lateral t t • j.i j • /^ „. .„ „ 



alveoli; other notations as in fig. "^'-"^''^^ ^''''' ^^ ^ho type Specimen. (See fig. 13a Plate 11). 

 14. Thejength of this posterior confluent cavity can be estimated 



from the slopes of the lateral alveoli, this being indicated in the restored longitudinal 

 section (text figure 14). 



The inner shell or siphuncular wall, is about 0..3 mm. in thickness and strongly 

 and regularly annulatcd upon the sides, these annulations forming an angle of approxi- 

 mately 82° with the dorsal surface, or 70'' with the pklne of the anterior endoconic blade. 



Fig. 1-"). CliildiociTds i-hiiKj- 

 iniiigli_ioei'ixi\ Diagrammatic cross- 



* The shell is oriented with the apex to the ol.iserver, the aperture or anterior end pointing away, and 

 the ventral side, (i.e. flattened side of endocone), downwards. The right and left sides then correspond to the observer's 

 right and left hand. In the figures on Plate II the position is reversed, so as to show the structure more clearly therefore 

 the references must also be reversed from those here given. 



