^^^- ^- C. C. Yu — Ordovician Cephalopoda of Central China (ii) 7 



the siphuncle. Their prolongations, called septal necks or septal funnels, are either short 

 as in Orthochoanites, or very long as in the Holochoanites. 



In Holochoanites as usually described there is another small axial tube existing in 

 the center of the siphuncle, which is called endosiphotube or endosiphuncle by Hyatt or 

 prosiphon by Zittel. The siphuncle is more or less solidly filled with thin calcareous 

 cones or endosiphosheaths around the endosiphuncle. There is a conical cavity formed 

 by the last endosiphosheath, which is termed endosiphocone or endocone by Hyatt. It 

 extends forward into the open space of the siphuncle known as the endosiphocylinder 

 {endoconal or siphuncular chamber of Hyatt). The endosipholining is the additional 

 covering on the inside of the siphuncular wall which is composed of the septal funnels. 



Recently Prof. Grabau has shown that the so-called siphuncle of the Holochoanites 

 is homologous with the shell of the Orthochoanites, the endosipholining of the former 

 corresponding to the wall of the latter, and the endosiphosheaths to the septa. He has 

 proposed the following terms' for use in the shells of Holochoanites, which are adopted 

 in the present paper. 



Ectoconch The outer shell of former authors (exclusive of 



siphuncle) . 



Endoconch The siphuncle of former authors. 



Ectotheca The outer shell wall of authors. 



Endotheca The inner shell wall or endosipholining of authors 



(often absent). 



Ectosepta The septa of outer shell of authors. 



Endosepta The septa of inner shell or the endosiphosheaths of 



authors. 



Tubus (pi. tubi) The prolongations of the ectosepta homologized by 



former authors with the septal funnels of the 

 Orthochoanites. 



Endosiphuncle The siphuncle of the endoconch or endosiphuncle of 



authors. 



Endocone Terminal conical living chamber of endoconch or 



endosiphocone of authors. 



Endocylinder The endosiphocylinder of authors. 



I. These terms have been published in the Bulletin of the Geological Society of China, Vol. 8 

 No. 2, p, ii8. 



