BIOMETRIC ANALYSES OF NUMMULITES PTUKHIANI KACHARAVA,Z.D., 1969 AND NUMMULITES FABIANII (PREVER IN FABIANI, 1905)

Eight populations of microspheric and megalospheric individuals belong ing to the species Nummulites ''ptukhiani'' (uppermost middle Eocene) and N. fabianii (upper Eocene) from northern Italy, Spain and Romania are described and discriminated biometrically. This distinction permit s recognition of the middle/upper Eocene boundary in shallow carbonate platform facies, The name N. ''ptukhiani'' as used here applies only to the western European ancestors of N. fabianii, with N. ptukhiani fr om Armenia being a separate species. In the megalospheric generation, test size, ornamentation, and external form show no direct correlation with geologic age and may have been paleoenvironmentally controlled. On the contrary, the examined B forms of N. ''ptukhiani'' are substant ially smaller and more inflated than the N, fabianii B forms, Moreover , the ornamentation pattern of N. ''ptukhiani'' B (reticulated, granul ated) is easily distinguishable from that of N. fabianii B (sinuous to meandering reticulate, non-granulated). For the megalospheric individ uals, internal features seem more independent of the paleoenvironment, but they may also have been environmentally controlled in some cases. Four parameters are used to distinguish the A forms: protoconch heigh t, shape of the embryonic apparatus, mean chamber length, and coiling curves. None of these internal features has been found useful to disti nguish between the B forms of the two species. Only the total number o f whorls is different (two to seven more whorls in N. fabianii B than in N. ''ptukhiani'' B). The overall similarities between the two speci es and the gradual transition of the measured features confirm they ar e successive chronospecies that can, however, be separated by conventi onal limits, useful for biostratigraphy of the middle/upper Eocene car bonates of the Tethys.