This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 19}\otimes\mathrm{Sym}^{ 18 }$. The following table gives the dimensions of various subspaces of $M_{19, 18}(\mathrm{Sp}(4, \mathbb{Z}))$.

Total30
Non cusp0
Cusp30