Pseudovorticella zhengae n. sp., P. difficilis (Kahl, 1933) Jankowski, 1976, and P. punctata (Dons, 1918) Warren, 1987, three marine peritrichous ciliates from north China. European Journal of Protistology, 42(4), November 2006: 269-279. 270 [Zoological Record Volume 143]