IJEEKMANTOWN AND CHAZY FORMATIONS OF CHAMTLAIN BASIN 4O3 



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 sipliuncle is the calcareous tube containing the fleshy siphon. 

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

 the interseptal spaces. The 



Subventran 



Propioventran 



ExtrAc entroventrAn 



Centroventran 



Intracentroventrdin 



Ventrocsntren 



Centren 



Dorsocentren 



Int racent rod or san 



Centrodorsan 



Extracentrodorsan 



Propiodorsan 



Subdorsan 



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 cctosiphuuclc 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 endosiphocylinder (Hyatt's 

 endoconal or siphuncular 

 chamber). 



It is followed apicad by the endosipliocone, a conical extension of 

 the same cavity, bounded by the endosiphosheath (Hyatt's endocone). 



The endosiphocone is continued in forms with organic deposits in 

 a tube to the apex; this tube is the endosiphotuhe (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 endosiplwcoleon. The endosiphotuhe and endosi- 

 phocoleon may be suspended by membranes (endosiplioblades) . 



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) 



Fi, 



Diagram to explain the terminology used 

 in describing the position of the siphuncle. 

 (Copy from Hyatt) 



