Abstract: Since the description of Neopsylla hongyangensis Li, Bai & Chen,1986 from Haiyuan and Helan Mountain in Ningxia had been published, specimens that identified as N. bidentatitorrnis of Qinghai, Gansu and Shanxi were re-examined.We found that most of them were mis-identified. They are really N. hongyangensis instead of being N. bidentatiformis. While N. bidentatiformis is a flea of medical importance, the geographical distribution, host preference and the identification characters of N. hongyangensis are presented and discussed for comparison. 1. N. hongyangensis belongs to the bidentatiformis group of the genus Neopsylla and is near to N. bidentatiformis, but could be readily distinguished from the later in the male, by the presence of a single median ventral arm branched from thebase of the distal arm of the 9th sternite. In the female, the anal styler is longer, being 3.4-3.7 times as long as broad at the base, instead of 2.5-3.0 times; and with fewer bristles on the 7th sternite, e. g. 5-6 in the main row, 14-16 smaller ones anteriorly instead of 7-9 in the main row, and 27-30 smaller ones anteriorly. The median sclerotized portion of the aedeagal crochet being pointed basaly is triangular in N.hongyangensis instead of being broad basaly, the membraneous flaps which vary in shape anterior and posterior to the sclerotized median portion. 2. N. hongyangensis is Palaeoarctic with the altitute of 1 500-5 O00M, while N. bidentatiforrnis is below I 50OM. Above sea level. 3. N. hongyangensis has a Iow host-specificity, and Cricetulus longicaudata, C.Migratorius, C. triton are the main hosts. Others are:species of the genera Alpodemus, Rxitus, Niviventer, Mus, Marmota etc. 4. N. bidentatiformis is a potential vector of plague. While N. Hongyangensisis systematically near to it, and had been mixed up with N. bidentatiformis, it coued caue a new problem for the endemic diseaes research and control workers.

Key words: Neopsylla hongyangensis Li, Bai & Chen, Neopsylla bidentatiformis (Wagner), aedeagal crochet, distal arm of the 9th sternum, ventral arm