This is the date shown in a Published (book) Transcription of a Marriage entry in a Catholic Register (not available online), So far all my friends who have tried it have come to the same conclusion I have which is that the priest's knowledge of Latin was not so much Dog as Mongrel!
"1870 primo dei decima nona Mensis February"
Yes, it does say February not Februarsis, but is that the transcriber or the original? To add to the confusion the marriage appears in the GRO index as having occurred in the March Quarter 1871!
Before I give up and buy the certificate can anyone find an alternative translation to a French priest trying to translate 19th February 1870? I did come up with a an alternative possibility based on the Roman Calendar of the Tenth day before the Nones of February, but that is invalid?