. Bulletin of the British Museum (Natural History). 306 C. P. NUTTALL 403a. 406a 406b 407 408 Figs 403-408 Pachydon ovalis sp. nov. Late Caenozoic; La Tagua, Colombia. 403, LL27872, holotype, a left valve; km upstream from La Tagua; Weeda Colin, a, external, x 3; b, internal, x 5. 404, LL28092, paratype, left valve; same locality as holotype; internal view, x 10. 405, LL27881, paratype, left valve; Loc. 33/480-560, x 4. 406, LL27880, paratype, right valve; Loc 54; Eden Colin, a, external; b, internal, x 4. 407, LL28094, paratype; from type locality; internal view of right valve f
. Bulletin of the British Museum (Natural History). 306 C. P. NUTTALL 403a. 406a 406b 407 408 Figs 403-408 Pachydon ovalis sp. nov. Late Caenozoic; La Tagua, Colombia. 403, LL27872, holotype, a left valve; km upstream from La Tagua; Weeda Colin, a, external, x 3; b, internal, x 5. 404, LL28092, paratype, left valve; same locality as holotype; internal view, x 10. 405, LL27881, paratype, left valve; Loc. 33/480-560, x 4. 406, LL27880, paratype, right valve; Loc 54; Eden Colin, a, external; b, internal, x 4. 407, LL28094, paratype; from type locality; internal view of right valve fragment showing cardinal tooth and resilium pit on hinge plate with pedal retractor scars below, x 15. 408, LL28093, paratype; from type locality; fragment of left valve of juvenile specimen, x 10. are paratypes; all Late Caenozoic of La Tagua district: LL28090-5, from type locality. Remainder all Eden colln; LL27880, Loc. 54; LL27881-3 (block), Loc. 33/480-560 cm; LL27906 (block), Loc. 33/560 cm. Name. 'Egg-shaped, oval.' Diagnosis. Small, oval, almost equivalve Pachydon; um- bones not prominent, slightly anterior to mid-length; denti- tion comparatively weak: pallial sinus deep. Distribution. Late Caenozoic, La Tagua Beds; La Tagua, Colombia, only. Description. The description is based on single, dissoci- ated valves, but it is clear that the species is virtually equivalve and the ventral commissure shows signs of only a weak flexure. The oval growth lines are modified posterodor- sally by a weak, somewhat crassatelliform truncation, but no corselet is differentiated. The slightly prosogyrous umbones are neither prominent nor strongly curved. Internal features of the left valve are known from the holotype, and the paratype LL28092 from the type locality: those of the right valve are known only from paratype LL27880. In this speci- men the cardinal tooth is damaged, but appears to lie in a dorsoventral plane. A long anterior lateral tooth lies parallel to and separated from th
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