M . L . Thompson ( 1964 ) gives the following diagnosis : Shell large, fusiform to irregularly cylindrical, planispiral, involute in most, irregularly uncoiled in some; spirotheca thick, composed of tectum and alveolar kariotheca; septa fluted in end zones of primitive genera, fluted completely across shell and to tops of chambers of more advanced genera; tummel singular in most forms, multiple in one genus; axial fillings absent to massive; chomata massive to slight.
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