Key to the British Throscidae
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Eyes without a clear incision; at most weakly sinuate adjacent to the antennal insertions. Metasternum with a clear longitudinal groove either side to accommodate the hind tarsi. Longitudinal raised ridges between the eyes diverging posteriorly.
Front margin of eyes distinctly incised. Metasternum without lateral grooves.
Frons smooth and evenly convex; without longitudinal ridges.
Frons with a pair of longitudinal raised lines, specimens must be examined carefully as this character is sometimes only weakly developed.
Longitudinal lines on the frons well developed and obvious. Eyes only weakly incised, the incision not extending half way and leaving at least 5 facets connecting the dorsal and ventral parts of the eye.
Longitudinal lines on the frons less distinct and sometimes difficult to see, low angle lateral lighting is the best way to see them. Eyes incised to beyond the middle; the dorsal and ventral parts connected by only 2 or 3 facets.
Size smaller, 1.9-2.3mm. Longitudinal lines on the frons weak, sometimes reduced to an interruption of the cuticle. In males the fine hairs along the lateral margins of the elytra are fine and difficult to discern; the mesotibiae have a group of setae, resembling a small spur, on the outer margin in the basal half.
Size larger, 2.5-3.0mm. Longitudinal lines on the frons distinct and clearly visible although sometimes flattened. In males the fine setae along the lateral margins of the elytra are obvious and the metafemora lack the group of setae on the outer edge. The form of the pronotum is also dimorphic; in the male the lateral margin is often weakly sinuate while in the female it is smoothly rounded.