On Coble surfaces and their automorphisms

Given a complex Coble surface $X$ with irreducible boundary $C$, we consider a specific automorphism $T:X\to X$, initially defined by Pompilj. We show that there are two families of Coble surfaces satisfying the condition $T{\mathrm{\mid }}_C={\mathbb{1}}_C$. Every Coble surface $X$ in the first family in nodal, and moreover the stronger equality $T={\mathbb{1}}_X$ holds. Meanwhile, the second family is ‘‘small’’, since it has codimension $3$ in the moduli space of Coble surfaces.