This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 18}\otimes\mathrm{Sym}^{ 2 }$. The following table gives the dimensions of various subspaces of $M_{18, 2}(\mathrm{Sp}(4, \mathbb{Z}))$.
| Total | 4 |
| Eisenstein | 1 |
| Klingen | 1 |
| Maass | 2 |
| Interesting | 0 |
The following samples live in this space.
18_C