  The pole structure of the $\Lambda(1405)$ is examined by fitting the
couplings of an underlying Hamiltonian effective field theory to cross sections
of $K^- p$ scattering in the infinite-volume limit. Finite-volume spectra are
then obtained from the theory, and compared to lattice QCD results for the mass
of the $\Lambda(1405)$. Momentum-dependent, non-separable potentials motivated
by the well-known Weinberg-Tomozawa terms are used, with SU(3) flavour symmetry
broken in the couplings and masses. In addition, we examine the effect on the
behaviour of the spectra from the inclusion of a bare triquark-like
isospin-zero basis state. It is found that the cross sections are consistent
with the experimental data with two complex poles for the $\Lambda(1405)$,
regardless of whether a bare baryon basis state is introduced or not. However,
it is apparent that the bare baryon is important for describing the results of
lattice QCD at high pion masses.
