Wikipedia
Bathmoceratidae
Bathmoceratidae is a family of ellesmerocerid nautiloids containing rather large straight or faintly exogastric (upwardly curved) shells and rather large ventral siphuncles with long septal necks and connecting rings that thicken inwardly into lobes that extend forward for the length of two or three chambers. The family was established to contain the genus Bathmoceras which is defined by the characters ascribed to the family.
Eothinoceras, sometimes included does not belong.