はつかねずみじゃなかったです
二十日鼠じゃなかったです
hatsukanezumijanakattadesu

Noun
Desu Copula

The polite, past negative form of はつかねずみ

1. Wasn't a mouse on the twentieth.; Wasn't a rat on the twentieth.

Past/Perfective
Negative
Polite
Casual Register
Usually Written in Kana