. Bulletin of the British Museum (Natural History). PEBASIAN MOITUSCAN FAUNAS SI'I. Figs 385-388 Pachydon erectus elongatus (Boettger). Pebasian; Pichana, Peru; Hauxwell Colin. 385, LL28083; a, b, left valve, side and dorsal views, x 10. 386, LL28081; a, right valve, side, x 10; b, dorsal view, x 10; c, front, x 20. 387, LL28080; left valve, x 10. 388, LL28082; a-c, internal views of broken right valve, all x 30. cither Pebas or Pichana, Peru (Hauxwell colln). In Senckenburg Museum, Frankfurt (not studied). Material studied. BMPD LL28080-5, Late Caenozoic, Pebasian; Pichana, Peru (Ha
. Bulletin of the British Museum (Natural History). PEBASIAN MOITUSCAN FAUNAS SI'I. Figs 385-388 Pachydon erectus elongatus (Boettger). Pebasian; Pichana, Peru; Hauxwell Colin. 385, LL28083; a, b, left valve, side and dorsal views, x 10. 386, LL28081; a, right valve, side, x 10; b, dorsal view, x 10; c, front, x 20. 387, LL28080; left valve, x 10. 388, LL28082; a-c, internal views of broken right valve, all x 30. cither Pebas or Pichana, Peru (Hauxwell colln). In Senckenburg Museum, Frankfurt (not studied). Material studied. BMPD LL28080-5, Late Caenozoic, Pebasian; Pichana, Peru (Hauxwell colln, extracted from matrix, 1982). No further records. Distribution. Restricted to Pebasian. Pebas or Pichana (Boettger 1878); Iquitos (de Greve 1938); probably Pichana (herein). Diagnosis. Differing from Pachydon erectus Conrad, , in being very small and elongate, with a length to height ratio of more than :1. Dimensions. In mm. 1 h br l/h Lectotype, Boettger's (1878) pi. 14, fig. 14, ? Pebas or Pichana. Paralectotype, Boettger's (1878) pi. 14, fig. 1, ? Pebas or Pichana. Iquitos (de Greve 1938: 40). (sv) Iquitos (de Greve 1938: 40). III (sv) Iquitos (de Greve 1938: 40). (sv) LL28080, Pichana. LL28081, Pichana. (sv) Description. The shell is small, apparently not exceeding 8 mm in length. The umbones are situated well anterior to mid- length of the shell. Outline crassatelliform, with a corselet separated from the main flank of the shell by a comparatively weak diagonal ridge of variable strength. The posterior tends to be truncated to some extent. The shell is virtually equivalve, and the commissure straight, as far as can be ascertained. In vertical view, the shell is rather stout. Remarks. Unfortunately, there is no good, continuous, growth series of P. erectus available for study. However, the impression gained from the Hauxwell Collection is that t
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