Contacyphon palustris

This genus was formerly known as Cyphon and many references have this species listed as Cyphon palustris.

Like the much commoner Contacyphon coarctatus, this species differs from most other Contacyphon in having 3-4 faint ridges along the elytra, however these are really hard to see. I can't honestly say that I could see them from the top (at any angle) but their presence was implied by the sharp straight borders to zones where the light reflected differently, these zones being located consistently no matter what angle the beetle was held to the light. The lines were more easily visible from the underside of the elytra after the elytra was removed.

Like coarctatus, the male aedeagus has apical processes including claws, the total length of which is about equal to the base on coarctatus and much smaller on palustris. On this specimen they were not as proportionately short as shown in the diagram in Duff, but clearly shorter than the base. To remove any doubt, the direction the claws points differs too - in coarctatus curved in the opposite direction to the base but here in palustris curved in the same direction as the base (and more outward).

male Contacyphon palustris showing its aedeagus (ventral section at two angles and dorsal section), sternite 9 and tergites 8 & 9, North Elmham Cathedral Meadows (Norfolk, UK), 2nd July 2021