Bulimus demerarensis was described by Pfeiffer (1861: 24) from Demerara (now part of Guyana). Drymaeus (Leiostracus) ruthveni was described by H.B. Baker (1926: 48) from the same region (Dunoon) and later was synonymised with Leiostracus (Leiostracus) demerarensis (Pfeiffer 1861) by Breure (1978: 1, 227). Troschel (1849) probably dissected this species under the name Bulimus cinnamomeolineatus, but illustrated only the jaw and the radula. The anatomy of this species remained unknown until 1997 when one snail has been collected alive in French Guiana. Unfortunately, this specimen dried out and had to be re-hydrated in a solution of tri-sodium phosphate. Surprisingly, the re-hydration worked quite well and we are able to illustrate the genital apparatus of this species for the first time. As the result, we are transferring demerarensis Pfeiffer 1861 (syn. ruthveni Baker 1926) from Leiostracus Albers 1850 to Bostryx Troschel 1847.