KEY TO GENERA WITHIN THE ORDER PLEUROSTOMATIDA Based on previous reports (Wu et al., 2017; Pan et al., 2020) and the present work, a revised key to the genera is provided here:

1. Glabrous region in anterior of right side present …............................................................................. 2

Glabrous region in anterior of right side absent …............................................................................... 4

2. Leftmost left kinety (LK n) terminates at anterior end of cell …........................................................... 3

Leftmost left kinety (LK) does not terminate at anterior end of cell ...........................… Pseudolitonotus

n

3. Right somatic kineties anteriorly shortened along rightmost full kineties …..................... Apolitonotus

Right somatic kineties progressively shortened anteriorly from middle towards dorsal and ventral margins …............................................................................................................................ Paralitonotus

4. Middle right somatic kineties anteriorly shortened to form a suture …............................................. 5

Middle right somatic kineties not shortened to form a suture ….......................................................... 10

5. Middle right somatic kineties shortened posteriorly to form a suture …..................... Kentrophyllum

Middle right somatic kineties not shortened posteriorly to form a suture .......................................... 6

6. Spoon-like excavation in anterior region present …........................................................ Amphileptiscus

Spoon-like exca vation in anterior region absent…...................................................................................7

7. Left perioral kinety forming a circle …................................................................................... Opisthodon

Left perioral kinety not forming a circ le ….................................................................................................8

8. Right and left perioral kineties do not cross and reach posterior of cell ….......................................... 9

Right and left perioral kineties cross and do not reach posterior end of cell …................ Apoamphileptus

9. Oral slit extends nearly to posterior end of cell …....................................................... Pseudoamphileptus

Oral slit does not extend nearly to posterior end of cell …..................................................... Amphileptus

10. Right somatic kineties anteriorly shortened along rightmost full kineties ….................... Protolitonotus

Right somatic kineties anteriorly shortened along perioral kinety.................................................... 11

11. Extrusomes absent along dorsal margin ….......................................................................................... 12

Extrusomes present along dorsal margin …....................................................................................... ... 13

12. Spoon-like excavation present …................................................................................................ Acineria

Spoon-like excavation absent …..............................................................................................., Litonotus

13. Without string-like oral bulge ….......................................................................................... Loxophyllum

With string-like oral bulge…........................................................................................... Siroloxophyllum