  Motivated by the superconductivity of $M_x$Bi$_2$Se$_3$, we study topological
excitations in a nematic superconductor using Ginzburg-Landau theory. An
isolated excitation at low field is shown to be either a distorted phase vortex
or a tightly-bounded pair of half quantum vortices. Close to upper critical
field $H_{c2}$, the vortex lattice is shown to be always hexagonal in the
extreme type-II limit. Due to the different symmetries of the vortex lattice
states, at least two phase transitions must take place when the external field
is lowered from $H_{c2}$.
