SYNOPSIS. Leptomonas costoris n. sp. is described from Gerris comatus. It differs from other species of Leptomonas in the structure of the reservoir which has ultramicroscopic thickenings in its wall, matched by corresponding thickenings in the adjacent flagellar membrane. The one or two diagonal lines seen in the reservoirs of Giemsa-stained specimens are thought to be manifestations of these ultramicroscopic fibrils. The reservoir structure suggests a close relationship between this species and Cryptobia, (family Bodonidae) in which somewhat similar structures have been described.
Blastocrithidia veliae is redescribed and differentiated from B. gerridis.