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Subfamily Omaliinae

Members of this subfamily are easily known by the presence of a pair of pale mounds ('ocelli') on the surface of the head on or near a line drawn through the posterior margin of the eyes. The elytra are usually longer than those of most other staphylinids, those members covering about one-half of the abdomen. Micralymma, an exception, has very short elytra. Six genera are known with marine species, but only three are included in the following key:

KEY TO GENERA OF MARINE OMALIINAE

I. Elytra about as wide as long......................................................................... Micralymma

Elytra longer than wide............................................. .....................................................2

2. Head strongly produced in front of eyes. ....................................................Arpediomimus

Head not strongly produced in front of eyes.........................................................Omalium

Macralymma Cameron. This genus is not adequately described and so cannot be included in the key. The single species M. punctiventris Cameron (1945) is said to be maritime from New Zealand.

Nesomalium Steel. Four species from the seashore of Campbell Island and Auckland Island in the sub Antarctic. Judging from the original description, this genus is not separable from Omalium.

Omaliomimus Jeannel. Two species from the seashore at Campbell Island. Like Nesomalium this genus appears to be inseparable from Omalium.

Micralymma Westwood. Members of this genus are confined to the northern part of the North Temperate Zone. They are circumpolar in distribution. Five species have been described from Siberia, Northern Europe, Greenland and Maine. They are submarine in habits. Species of this genus are readily distinguished by their very short elytra which cover no part of the abdomen. The British species M. brevipenne Gyllenhal is black, strongly alutaceous and about 3 mm long.

Arpediomimus Cameron. This genus is said to be close to Omalium but has the head produced forward of the eye for at least the length of the eye. Only two species are known from the sub Antarctic island. A. faulklandicus Cameron from the Falkland Islands is yellowish brown and 4.5-5 mm long. It lacks ocelli. A. kronei Kiesenwetter from Campbell Island is dark brown and 5-8 mm long. It has ocelli. The genus was reviewed by Steel (1964).

Omalium Gravenhorst. More than one hundred species have been described in this genus mostly from decaying organic matter in the Temperate Zones. Four species are known from seaweed from the British Islands and one from Pacific North America. They are reddish brown and 2-4 mm long. Members of this genus are particularly characterized by a longitudinal carina on the mesosternum.