Fustiaria

Fustiaria is a genus of scaphopods in the order Dentaliida and is the only genus comprising the family Fustiariidae, with 24 species. 
Description.
The shells of "Fustiaria" are characterized as smooth, slender, circular in cross section, slightly curved, thin-walled, and virtually transparent. The central tooth of its radula (chewing organ), called a "rachis", is unusual compared with that of other Dentaliids in that it is flat on its tip rather than pointed. The space around the foot (the "pedal sinus") is divided by a thin horizontal membrane called a septum.