The coral fauna of various localities In Northern Apennines shows that the isolation of the Mediterranean at the end of the Miocene period (Messlnian) deeply affected the geological and biological history of the Tethys during and after the "salinity crisis". The coral fauna includes several species (Flabellum berti, Stephanocyathus strobeli, Caryophyllia communis, Caryophyllia fetsinea, etc.) which are similar to deep water species of the present N-E Atlantic. The presence of these corals In the earliest Pliocene period of the "Mediterranean" together with other deep-and-cold water forms involves hydrologic conditions similar to those occurring at present in the N-E Atlantic, possibly by an Intercommunication between the Ocean and the Tethyan Sea which was deeper than the Recent Gibraltar threshold.