Protatlanta rotundata differs considerably from the type of the genus, Protatlanta souleyeti. Not only does the adult shell in Protatlanta rotundata reach a diameter that is roughly five times that of Protatlanta souleyeti, but the morphology of its protoconch and the shape of the fully grown shell are utterly different. Also, as both species occur together in the Pangasinan samples, Protatlanta rotundata can certainly not be considered to be the ancestor species. The presence of a subperipheral belt much the same as in Protatlanta souleyeti, on the other hand, demonstrates that a conchiolin keel has been present in this species.
