Typhloesus wellsi (see, for example, Melton & Scott (1973)) is a bizarre metazoan from the mid-Carboniferous (Namurian) of central Montana, U.S.A. Typhloesus gen. nov. is erected here, because the previous generic names used to describe this animal refer to conodonts, enclosed within the alimentary canal, that were ingested as a result of predation. All these names are invalid in the present context. Its fusiform body (maximum length ca. 90 mm) bore a paired ventral keel, interrupted at about two thirds of its length by a conspicuous break. At the posterior a prominent fin was supported by two sets of orthogonally disposed fin rays in an arrangement unique to this animal. The exterior lacked other appendages, although lateral fins may be inferred on hydrodynamic grounds. The internal anatomy consisted of an elongate foregut and a voluminous midgut. The mouth was ventrally directed and apparently large. The gut appears to have been blind, lacking a hind section and an anus. Located beneath the central midgut was a remarkable organ composed of two discs, known as the ferrodiscus, and attached to the ventral margin. Its function is obscure, but its association with possible circulatory vessels suggests a role in storage or respiration. Obscure traces of possible mesenteries, longitudinal muscles and a cuticle are discussed. Typhloesus gen. nov. is interpreted as an active swimmer, with lateral propulsive oscillations, probably largely confined to the posterior area where the rigid fin is inferred to have played an important role. Gut contents of conodont apparatuses, variously disarticulated, fish and worm teeth suggest this animal was a predator and scavenger, competing with other members of this trophic group in the shallow waters of the Bear Gulch `lagoon'. Previous suggestions that Typhloesus gen. nov. is a chordate cannot be supported, but the phyletic affinities of this extraordinary creature are unresolved. It joins a select group of late-Palaeozoic animals whose peculiar appearance prohibits convincing comparisons with known phyla. These species, none of which is closely related to any of the others, could be survivors from the `Cambrian explosion' in which a multitude of bizarre body-plans evolved, or they could represent the results of adaptive radiations nearer to the Carboniferous. Absence of ancestors and taphonomic bias in favour of soft-part preservation in nearshore environments makes it difficult to resolve these possibilities, but the latter option is tentatively preferred.