This paper extends our knowledge of the higher excited states of the ammonia molecule by presenting detailed measurements of the 2 + 1 resonance enhanced multiphoton ionization (REMPI) spectrum of both NH3 and ND3 obtained following excitation in the wavelength range 298-242 nm, i.e., at energies up to the first ionization energy. Complementary analyses of the wavelength resolved REMPI spectrum and the accompanying REMPI-photoelectron spectra leads to the identification of ten new Rydberg origins of NH3 (four for ND3) with principal quantum numbers n less than or equal to 8 and, in most cases, of the accompanying out-of-plane bending vibrational progression. Symmetry assignments for the various newly identified excited states an offered, based on band contour simulation and/or quantum defect considerations. Dominant amongst these are the (E) over tilde" (1)A"(2) (5s alpha＇(1) <-- 1 alpha"(2)) state : upsilon(0) = 74118(2) cm(-1) [NH3], upsilon(0) = 74258(2) cm(-1) [ND3], the (F) over tilde" E-1" (5pe＇ <-- 1 alpha"(2) state : upsilon(0) = 76220(50) cm(-1) [NH3], upsilon(0) = 76240(50) cm(-1) [ND3], the (F) over tilde＇ (1)A＇(1) (5pa"(2) <-- 1 alpha"(2)) state : upsilon(0) = 76674(1) cm(-1) [NH3], upsilon(0) = 76770(5) cm(-1) [ND3], and the (G) over tilde＇ (1)A＇(1) (6pa"(2) <-- (1) alpha"(2)) state : upsilon(0) = 78494(1) cm(-1) [NH3]. The present work serves to reinforce the previously noted dominance of np <-- 1 alpha"(2) Rydberg excitations in the 2 + 1 REMPI spectrum of ammonia. In addition, the adiabatic ionization energy of ND3 is estimated to be 82280 +/- 40 cm(-1) based on the assumption that analogous Rydberg states of NH3 and ND3 will have very similar quantum defects.