Key to species of Siamopsis gen. nov.

1. Dorsal margin of Cp in lateral view flat at mid length …………………………………………2

– Dorsal margin of Cp in lateral view arched at mid length ……………………………………3

2. Postero-dorsal plate of LV in internal view broad, with a small tooth-like tubercle on anterior part, RV in internal view with tubercle-like structures under postero-ventral inner list ………… ……………………………………………………………………… S. khoratensis gen. et sp. nov.

– Postero-dorsal plate of LV in internal view elongated, without tooth-like tubercle, RV in internal view without tubercle-like structures under postero-ventral inner list … S. planitia gen. et sp. nov.

3. Cp in lateral view subtriangular, postero-dorsal plate of LV in internal view broad, with two small teeth-like tubercles on margin, RV in internal view without tubercle-like structures under postero-ventral inner list …………………………………………… S. renateae gen. et sp. nov.

– Cp in lateral view elongated, postero-dorsal plate of LV broad or elongated, RV in internal view with tubercle-like structures under postero-ventral inner list ………………4

4. Postero-dorsal plate of LV in internal view broad, with tooth-like tubercle in the middle ……………………………………………………………………… S. conspecta gen. et sp. nov.

– Postero-dorsal plate of LV in internal view elongated, with tooth-like tubercle on posterior margin ………………………………………………………………… S. suttajiti gen. et sp. nov.