On the foraminiferal genera Tritaxis Schubert and Trochamminella Cushman (Protozoa: Foraminiferida) P. Bronnimann 9G, Chemin de Bedex, 1 226 Thonex, Geneva, Switzerland J. E. Whittaker Department of Palaeontology, British Museum (Natural History), Cromwell Road, London SW7 5BD I. On Tritaxis Schubert The name Tritaxis was coined by Schubert (1920: 1 80) for triserial agglutinated post-Palaeo-zoic foraminifera which he considered to be the descendants of Tetrataxis Ehrenberg. Schubert expressed his reasoning as follows: ... die palaeontologisch primitiveren Formen Globivalvulina und Tetrataxis dagegen wandeln sich im Mesozoicum um: erstere in manche Globigerinen [sic] und von letzterer die einfachen Typen (z.B. die ohne extrem ausgebildete Nabelhohlung) durch starkere Sarkodenzunahme zunachst zu Formen, bei denen nicht vier, sondern nur drei Kammern einen Umgang aufbauen. Die letztere Verhaltnis scheint nun fur eine grossere Reihe von Formen konstant geworden zu sein, besonders fur die postpalaeozoischen und jiingsten sogar noch lebenden Vertreter (Fusca Will., conica P. u J.) die sich durch den Mangel einer zentralen Hohlung auch nicht unwesentlich von den karbonen Valvulinen, den Tetrataxisarten, unterscheiden; deshalb scheint sich auch ihre (etwa subgenerische) Abgrenzung von den karbonen etwa als Tritaxis zu empfehlen [our italics]. Tritaxis, born therefore in the course of speculations into the evolution of agglutinated foraminifera, was formalised taxonomically by Cushman (1928) who designated as its type species Rotalina fusca Williamson, a trochamminid foraminifer from the Recent of the Bri-tish Isles (Williamson, 1858: 55, pi. 5, figs 1 14, 115). Now a genus within the Trochammini-dae Schwager, it was however immediately placed by Cushman (1928: 171) into synonymy with Trochammina Parker & Jones (type species: Nautilus injlatus Montagu, 1808, from the Recent of SW England). Cushman (1948: 202) subsequently did not change this opinion and listed, in the fourth edition of his Foraminifera. Their classification and economic use, Tritaxis as a synonym of Trochammina. This was also accepted by Bermudez & de Rivero (1963). Glaessner (1945: 99) considered Tritaxis as a separate subgenus of Trochammina characterised by a low, conical test, and included within it Jurassic and Recent species (see discussion in Bermudez & de Rivero, 1963: 318). It was Loeblich & Tappan (1955: 19) who reinstated Tritaxis as a valid genus. They amended it to include low trochoid trochamminid tests with at first 4 chambers per whorl, then only 3 in the final whorl; free-living in early ontogeny and attached in the adult stage, with an areal ovate aperture in the free-living forms and a tubular aperture in the attached. These authors stated that . . . 'the types of Williamson's species are missing from the British Museum Collections', and based their emended definition of Tritaxis on specimens labelled Tritaxis fusca (Williamson) encountered in the F.C. Helga haul no. SR 331 from off SW Ireland, depth 610-680 fathoms (1 1 15-1245 m), deposited in the collections of the United States National Museum (USNM), reg. nos P 2198a, b. The two hypotypes illustrated by Loeblich & Tappan (1955: pi. 3, figs 5a-c, 6) have been examined by one of us (P.B.) who Bull. Br. Mus. nat. Hist. (Zool.) 46(4): 291-302 Issued 31 May 1984
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