This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 20}\otimes\mathrm{Sym}^{ 26 }$. The following table gives the dimensions of various subspaces of $M_{20, 26}(\mathrm{Sp}(4, \mathbb{Z}))$.
| Total | 80 |
| Non cusp | 3 |
| Cusp | 77 |