The Middle Ordovician (Darriwilian) echinoderm fauna of Bang Mueang Song Tho, western Thailand (Pha Phum group, Bo Ngam Formation(?)), includes rare thecae, and common thecal ossicles and columnals, and is dominated by 'cystoids'. Cheirocrinid glyptocystitoids include Cheirocystella sp. (= Echinoencrinites sp. aff. E. senckenbergii (von Meyer) sensu Wolfart), 'Cheirocrinus' sp. and Cheirocrinidae incertae sedis. Hemicosmitoids are composed of Paracaryocrinites kochi (Wolfart), 'Paracaryocrinites' sp. and Polycosmites sp. cf. P. kaekeli Wolfart. The aristocystitid Sinocystis sp. cf. S. loczyi Reed is the only diploporite. Columnals of Bystrowicrinus (col.) sp. are probably crinoidal. The fullest determination of the echinoderm biodiversity of this site has been obtained using all specimens from single ossicles to articulated thecae. The limited taphonomic data suggests that the echinoderm assemblage is parauthochthonous. Other echinoderms described from coeval deposits in this region include Stichocystis thailandica Wolfart; Heliocrinites sp. aff. H. qualus Bather (probably a Lophotocystis Paul); Gomphocystites? sp. indet. (= trilobite?); Codiacystis sp. aff. C. bohemicus (Barrande) (= bryozoan?); Aristocystis [sic] sp. A of Paul; and [non] Incertae sedis sp. C of Paul (may not be an echinoderm).