Descriptions of three new taxa in the genus Davidius Selys from Shaanxi, China (Anisoptera: Gomphidae)

D. miaotaiziensis sp. n. (holotype China, Shaanxi: Miaotaizi. I2-VI-I986; allotype $: same locality, 13-VI-I987), D. yuanbaensis sp. n. (holotype China, Shaanxi: Yuanba. Vl-1983), and D. davidi shaanxiensis ssp. n. (holotype $: China, Shaanxi: Miaotaizi, 1X-I984; allotype 2: same locality, I5-VI-I987) are described and figured. The latter is similar to D. d. assamensis Laidlaw, from which it differs by the unmarked 3 distal abdominal segments and by the sternal processes on segments 7-9. — The types are deposited in the Department of Biology, Hanzhong Teachers College.