Two specimens of a large Thais collected near Cape Blanc, Mauritania, were considered to belong to a new species and were described as Thais (Stramonita) hidalgoi by Coen (1946: 39). He did not designate a holotype nor did he figure the new species. However, Coen gave the length and width of one of the specimens as 97 and 67 mm respectively. Both type specimens are present in the Coen collection, which is now part of the mollusc collection of the Hebrew University of Jerusalem (HUJ). The specimen which fits Coen’s measurements, is here selected as lectotype of T. hidalgoi (HUJ 30.880/a). The smaller specimen, 94.4 x 58.2 mm, is the paralectotype (HUJ 30.880/b). In the description Coen compared T. hidalgoi with T. barcinonensis (Hidalgo, 1867), which is now considered a finely ribbed variety of T. haemastoma (Linnaeus, 1767) (see Nordsieck, 1968: 118). A study of various populations of T. haemastoma from the Mediterranean and West Africa revealed that T. hidalgoi is only a large variety of the former. The shells agree in every detail but size with typical T. haemastoma from Lobito Bay, Angola, as figured by Clench & Turner (1948: 2, figs. 3-4). Thais (Stramonita) hidalgoi Coen, 1946, is therefore considered a junior synonym of Thais (Stramonita) haemastoma (Linnaeus, 1767).