Key to species of Thiallela based on male genitalia

1. Lateral lobes of juxta obviously longer than apical process of gnathos........................................... 3

- Lateral lobes of juxta not longer than apical process of gnathos................................................ 4

2. Transtilla with middle area of posterior margin protruded in hillock shape, posterolateral processes narrowed and elongate (Li & Ren 2006, Fig. 5)........................................................................... T. naevilla

- Transtilla with middle area of posterior margin short-fingerlike protruded, posterolateral processes short and broad (Li & Ren 2006, Fig. 6)............................................................................... T. platantra

3. Apical process of gnathos trapezoidal (Yamanaka 2002, Fig. 4)......................................... T. hiranoi

- Apical process of gnathos tapered or spatulate............................................................. 5

4. Clasper extending to or near end of sacculus............................................................... 6

- Clasper extending beyond end of sacculus................................................................ 7

5. Apical process of gnathos spatulate; posterolateral processes of transtilla triangular (Fig. 9)............... T. epicrociella

- Apical process of gnathos tapered; posterolateral processes of transtilla auriform, bent inwardly (Fig. 11).................................................................................................... T. celadontis sp. nov.

6. Clasper not inflated ventroapically, without small spine dorsoapically; aedeagus with two clubbed cornuti (Fig. 10).................................................................................................... T. ligeralis

- Clasper slightly inflated ventroapically, with a small spine dorsoapically; aedeagus with numerous small, conical thorn-like and five horn-like cornuti (Fig. 12)..................................................... T. sulciflagella sp. nov.