. Bulletin of the British Museum (Natural History). 413b. Figs 413-414 Pachydon trigonalis sp. nov. Pebasian; Puerto Naririo, Colombia; Weeda Colin; right valves. 413, LL27860, holotype; a. b. external and internal views, x 6. 414, LL27861, paratype; a, external, x 10; b, internal, x 15; c, front, x 10; d. front oblique view of umbo and cardinal tooth, X 10; e, f, dorsal views showing cardinal tooth, x 40 and x 10; g, internal view obliquely from below, x 10. Pachydon trigonalis sp. nov. Figs 413-419 HOLOTYPE. A right valve, LL27860; Late Caenozoic; Puerto Naririo, Colombia (Weeda co
. Bulletin of the British Museum (Natural History). 413b. Figs 413-414 Pachydon trigonalis sp. nov. Pebasian; Puerto Naririo, Colombia; Weeda Colin; right valves. 413, LL27860, holotype; a. b. external and internal views, x 6. 414, LL27861, paratype; a, external, x 10; b, internal, x 15; c, front, x 10; d. front oblique view of umbo and cardinal tooth, X 10; e, f, dorsal views showing cardinal tooth, x 40 and x 10; g, internal view obliquely from below, x 10. Pachydon trigonalis sp. nov. Figs 413-419 HOLOTYPE. A right valve, LL27860; Late Caenozoic; Puerto Naririo, Colombia (Weeda colln). Paratypcs LL27861-70, over thirty separate valves and two complete juveniles, locality and horizon as holotypc; and LL28007, six juvenile shells, Canama, extracted in 1984 from matrix of Barrington Brown colln. Name. 'Triangular'. DIAGNOSIS. Subtrigonal, crassatelliform in outline, almost cquivalve Pachydon: umbones erect, at about mid-length. DESCRIPTION. The anterodorsal and posterodorsal margins slope downwards at almost the same angle. The anterior of the shell is well rounded. Posteriorly, a crassatelloid corselet is separated from the flank by a weak, well-rounded ridge. The ridge bordering a region analogous to an escutcheon is also very weak. The ventral margin is barely coin ex and its deepest point is in front of the umbones. The ventral commis- sure is also virtually straight and the two valves are of the same convexity. The centrally placed umbones are slight!) prosogyrous and touching. 1'hc socket and tooth are comparatively strong but narrow and vertical. The front of the tooth is exposed to the outside world underneath the anterior of the umbones. A shallow pallia! sinus is Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(N
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