Key to the Onycocaris quadratophthalma -like species

1. First pereiopod chela elongate, cylindrical, 7.7 times longer than width.......................... O. fujinoi Bruce, 2011

- First pereiopod chela less than 6.5 times longer than width..................................................... 2

2. Distolateral tooth of scaphocerite small, not exceeding lamella; eye quadrate, dorsal telson spines small.......................................................................................... O. quadratophthalma (Balss, 1921)

- Distolateral tooth of scaphocerite large, exceeding lamella; eyes subquadrate; dorsal telson spines normal............... 3

3. Major second pereiopod dactyl cutting edge with about 24 denticles, increasing in size distally, distal teeth coarse.................................................................................. O. hyamaensis Komai & Itou, 2012

- Major second pereiopod dactyl cutting edge minutely serrate, denticles sub-uniform................................. 4

4. Rostral tip not up-turned; eye quadrate; major second pereiopod dactyl with single low tooth; cutting edge minutely denticu- late; ambulatory dactyls with accessory tooth well developed, deeply acutely bifid.................. O. balsii Bruce, 2011

- Rostral tip up-turned, eye subquadrate; major second pereiopod dactyl with two low teeth; cutting edge entire; dactyls with accessory tooth feebly bluntly bilobed........................................................ O. maui sp. nov.