Mecodema rectolineatum

M. howittii measures between 26–31 mm (1.02–1.22 in) in length, making it the largest of the ten endemic ground beetle species found on Banks Peninsula. Its body is uniformly black, with a smooth and slightly depressed head vertex, and faint or absent punctures. The labium bears three punctures on either side at the base. The pronotum has 10–12 punctures along the lateral margins. The elytra exhibit flattened third and fifth intervals, while the other intervals vary in smoothness and punctation.

This species is restricted to the central and eastern parts of Banks Peninsula, occurring across both lowland and higher altitude sites. Historical records indicate that M. howittii once extended west to the Port Hills, but by the 1980s populations there had disappeared, possibly due to extensive nineteenth-century deforestation and predation by introduced mammals such as rats and mice. M. howittii inhabits remnants of podocarp and hardwood forest, as well as grassland and even in heavily modified habitats such as pasture. It is frequently found beneath logs, which provide microhabitats that retain moisture and shelter. Populations in pastures are believed to persist in relictual microhabitats where fallen wood remains. Although it was once very common in high ridges where forest had been cleared and logs left to lie in pasture, it disappears when the logs rot away or are burned.

M. howittii is nocturnal, emerging at night to hunt small invertebrates. It preys on larvae of other beetles, such as Holcaspis suteri, as well as crane flies and (in captivity) mealworms. Activity levels decrease when soil temperatures fall below 6.5 °C (43.7 °F). Females brooding eggs have been observed between December and January, suggesting breeding occurs during spring and early summer. Like other Mecodema, the species is flightless and lives in burrows or under debris on the forest floor.