This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 16}\otimes\mathrm{Sym}^{ 24 }$. The following table gives the dimensions of various subspaces of $M_{16, 24}(\mathrm{Sp}(4, \mathbb{Z}))$.

Total45
Non cusp3
Cusp42