. Bulletin of the British Museum (Natural History). 222 CP. NUTTALL. Fig. 185 Indeterminate gastropod, figured as Toxosoma eboreum by Bristow & Parodiz (1982: 42, fig. 16). Miocene, ivlangan Formation; Loc. CRB 36, Cuenca Basin, Ecuador; GG19816, x 10. Parodiz (in Bristow & Parodiz, 1982: 41, fig. 16) is not a Toxosoma. It has moderately coarse axial ribbing and indis- tinct traces of spiral threads. Both it and GG19815 come from the Mangan Formation at Loc. 36b, not 26b as quoted by Parodiz. G43325-6 (Carrion Colin), from the San Cayetano Formation of the Loja Basin, Ecuador
. Bulletin of the British Museum (Natural History). 222 CP. NUTTALL. Fig. 185 Indeterminate gastropod, figured as Toxosoma eboreum by Bristow & Parodiz (1982: 42, fig. 16). Miocene, ivlangan Formation; Loc. CRB 36, Cuenca Basin, Ecuador; GG19816, x 10. Parodiz (in Bristow & Parodiz, 1982: 41, fig. 16) is not a Toxosoma. It has moderately coarse axial ribbing and indis- tinct traces of spiral threads. Both it and GG19815 come from the Mangan Formation at Loc. 36b, not 26b as quoted by Parodiz. G43325-6 (Carrion Colin), from the San Cayetano Formation of the Loja Basin, Ecuador, were labelled by Parodiz as belonging to this species, but were not mentioned in Bristow & Parodiz (1982). The material consists of blocks of well-bedded buff marl rich in moulds of small gastropods which resemble this species in shape. They are, however, considerably smaller, with a maximum height of 2 mm, and have much smaller whorls. Unfortunately neither the shape of their growth lines nor the presence or absence of a columellar plait can be made out. Although these specimens might be Toxosoma, they are much more likely to be very young 'post-spat' of the smooth-spired Heleobia, which is common at certain horizons in the Ecuadorian non-marine Neogene. Family VITRINELLIDAE Bush, 1897 I am indebted to Dr W. F. Ponder (Australian Museum, Sidney) for the suggestion that the Pebasian fossil taxa dealt with below are best assigned to the otherwise fully marine family Vitrinellidae (Bush 1897: 122) rather than, as I had originally thought, to the fresh-water genus Coahuilix (Hydrobiidae). These fossil species, not necessarily con- generic at first sight, also bear some resemblance to the basommatophoran Superfamily Glaciodorbacea. In addition, earlier references in the literature to Pebasian species of Planorbis refer, at least in part, to the fossil taxa under consideration. The presence of small, virtually planorbiform, shells in several major groups means that correct fam
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