Meaning of this operator

 P: 134 What's the meaning (if any) to this operator defined by the series: $$\sum_{n=0}^{\infty} (-1)^{n}x^{n}\frac{d^{n}}{dx^{n}}$$ i think i have seen this operator before, but i can't remember when or why. perhaps related to the "Theta" operator $$\Theta = x\frac{d}{dx}$$