This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 18}\otimes\mathrm{Sym}^{ 6 }$. The following table gives the dimensions of various subspaces of $M_{18, 6}(\mathrm{Sp}(4, \mathbb{Z}))$.
| Total | 9 |
| Non cusp | 2 |
| Cusp | 7 |