. Bulletin of the British Museum (Natural History). Figs 35-38 Recent Littoridininae. 35, Tryonia clathrata Stimpson, type species of Tryonia. BMZD ? Pleistocene; Colorado, ; x 12. 36, ?Tryonia coronata (Pfeiffer), usually referred to either Pyrgophorus or Lyrodes. BMZD 1984226. Recent; Venezuela; x 10. 37a, b, Durangonella mariae Morrison, 1945. BMZD , paratype; front, x 20; oblique view of apex, x 60. ?Subfossil; Tlahuac, , Mexico; pres'd Smithsonian Institution. 38a, b, Brachypyrgulina carinifera Haas. BMZD ; paratype; front, x 1
. Bulletin of the British Museum (Natural History). Figs 35-38 Recent Littoridininae. 35, Tryonia clathrata Stimpson, type species of Tryonia. BMZD ? Pleistocene; Colorado, ; x 12. 36, ?Tryonia coronata (Pfeiffer), usually referred to either Pyrgophorus or Lyrodes. BMZD 1984226. Recent; Venezuela; x 10. 37a, b, Durangonella mariae Morrison, 1945. BMZD , paratype; front, x 20; oblique view of apex, x 60. ?Subfossil; Tlahuac, , Mexico; pres'd Smithsonian Institution. 38a, b, Brachypyrgulina carinifera Haas. BMZD ; paratype; front, x ; oblique view of spire, x 50. Sucune, Lake Titicaca, Peru, depth 5 m. (1966: 179, 182 et seqq.) he accepted all of Haas' Lake Titicaca genera not only as distinct, but as belonging to two subfamilies, the Cochliopinae and Littoridininae. Moreover, Tryonia {sensu Taylor) would have a discontinuous geo- graphical range (Taylor 1966: 183, text-fig. 14, map), and though the pre-Pleistocene record is sparse, Taylor's list (made without comment) implies that Tryonia was flourishing in both North and South America before the existence of the Panamanian land bridge. The apparent adaptive radiations in Lakes Titicaca and Tanganyika may be taken as examples of what might be expected to occur in other groups, including fossils under consideration. There is, however, justification for the provi- sional classification of fossils on a slightly different, pragmatic, basis. None of the fossil species under consideration, includ- ing 'Littoridina' crassa (Etheridge), can be confidently assigned to living genera of Littoridininae as listed in Taylor (1966: 182-3). In the present paper Dyris is used for those species with predominently spiral sculpture and Liris is retained for those with predominently axial, as opposed to collabral, sculpture. This generic arrangement is perhaps somewhat arbitrary and cannot claim to be more than a workable compromise. This is partly dictated by lack of know
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