- 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
These genera "are shown to be different developmental stages of single biological units. Three of these units can be followed in their development passing through these artificial 'genera,' the stages having been named as different artificial 'species.' One unit began and ended in the Albian; a second one began in the Albian and ended in the upper Maestrichtian; and a third one began in the Danian and has not yet fully ended in the Recent. Such artificial genera have no taxonomic value, and appear to be totally invalid."