Key to species of Microlysias

1. Antenna 2 male, peduncular article 5 subquadrate, enlarged; gnathopod 1 length <2.1 x width; telson cleft about 65 % or less ................................................................................................... 2

- Antenna 2 male, peduncular article 5 subtriangular, enlarged; gnathopod 1 slender, length 2.5 x width; telson cleft 74 % of length............................................................................. M. triangulus sp. nov.

2. Eyes very large, irregularly subrectangular, occupying most of head; maxilla 1, inner plate with a slender spine projection apically; maxilla 2 plates stout.................................................. M. soela Lowry & Kilgallen, 2014

- Eyes ovoid, medium sized, not occupying most of head; maxilla 1, inner plate lacking a slender spine projection apically; maxilla 2 plates slender, of normal size....................................................................... 3

3. Male antenna 2, peduncular article 5, length=width; gnathopod 2, propodus very slender and curved, length 2.9 x width; pereopod 7, merus narrow; epimeral plates 2–3, posterior margins smooth; mandibular palp, article 1, length about 0.7 x article 3............................................................................... M. xenokeras Stebbing, 1918

- Male antenna 2, peduncular article 5, length 1.45 x width; gnathopod 2, propodus subquadrate, straight, length 2.1 x width; pereopod 7, merus expanded; epimeral plates 2–3, posterior margins microserrate; mandibular palp, article 1, length subequal to article 3........................................................................ M. rectangulatus sp. nov.