- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
The cardinal processes in the Productidae are classified as either bilobed or trilobed. Each type is described and figured as it occurs in several species, and the types are compared. The wide variation of the process in the species of Linoproductus and Avonia is particularly significant, and it is suggested that these genera are polyphyletic.