BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 403 



The conch, if not circular in section, may be either compressed 

 (when the transverse diameter has been shortened) or depressed 

 (when the dorsoventral diameter lias been shortened). 



The direction of the conch is designated as apicad (in apical 

 direction), orad (in oral direction), dorsad and ventrad. 



The apertural margin frequently possesses, besides the hyponomic 

 sinus, lateral expansions, termed crests or lappets. 



The siphuncle is the calcareous tube containing the fleshy siphon. 

 It may be tubular or nummuloidal (moniliform) ; i. e. inflated in 

 the interseptal spaces. The 



Subventran 

 Propioventran 

 Ext rac e nt rovent ran 

 Cent rove ntran 

 Int rac ent rove ntran 

 Ventrocentren 

 Centren 

 Dorsocentren 

 Int rac e nt rod or san 

 Centrodorsan 

 Extracentrodorsan 

 Propiodorsan 

 Subdors&n 



position of the siphuncle with- 

 in the phragmocone can be 

 precisely stated by the use of 

 the terms given in the ap- 

 pended diagram [text fig. i]. 



The cctosiphuncle is the ex- 

 ternal wall of the siphuncle ; 

 the endosiphuncle comprises 

 all structures within the same. 



The anterior or upper part 

 of large siphuncles remains un- 

 obstructed and was doubtless 

 occupied by an extension of 

 the mantle cavity. This part 

 of the siphuncle is here term- 

 ed endo sip ho cylinder (Hyatt's 

 endoconal or siphuncular 

 chamber). 



It is followed apicad by the endo sipho cone, a conical extension of 

 the same cavity, bounded by the endo sipho sheath (Hyatt's endocone). 



The endosiphocone is continued in forms with organic deposits in 

 a tube to the apex; this tube is the endosiphotube (endosiphuncle 

 Hyatt, prosiphon Zittel). Sometimes a wider broad flat tube, clos- 

 ing apicad into a double plate, extends apicad from the endosipho- 

 cone. This is the cndosiphocolcon. The endosiphotube and endosi- 

 phocoleon may be suspended by membranes (endosiphoblades) . 



The siphuncular wall or ectosiphuncle consists originally entirely 

 of the septal necks or funnels, which arise from the bending of each 

 septum apicad into a funnel around the point of origin of the 

 siphon. In most forms the septal necks are short and continued in 

 apical direction by a more or less porous wall (the septal segments) 



Fig 



Diagram to explain the terminology used 

 in describing the position of the siphuncle. 

 (Copy from Hyatt) 



