The nematode worms discovered by Mr Shipley in the swim-bladder of Trout belong to the species Cystidicola farionis, first described by Fischer, and considered by him to represent a new and distinct type in nematode structure for which he proposed the generic name Cystidicola. Later writers refused to accept the new genus and included it in various other groups (see Synonymy, p. 190). In accordance with an old nomenclatural practice the proposed generic name was adopted as the specific name in place of that originally given, thus Cystidicola farionis became, for Rudolphi, Spiroptera cystidicola. From a detailed examination of the various characters of C. farionis I have come to the conclusion that Fischer was correct in creating a new genus for the new forms, and I therefore propose the reinstatement of the abandoned name Cystidicola. It is also in accordance with modern nomenclatural ruling that the original specific name farionis should be adopted in place of cystidicola.