During investigations on Paratetranychus pilosus[Panonychus ulmi], C. & F., on apple in Connecticut, collections were made of all the mites that occurred on the trees. Lists are given of some 30 species found, of which at least seven were plant feeders, at least 13 predacious and the rest scavengers or of doubtful habits. The only serious pests were P. pilosus, which is consistently of importance, and Tetranychus bimaculatus[Tetranychus urticae], Harvey, which has become increasingly injurious since the use of DDT by growers. The predators described include Gamasellus americanus, Iphidulus fallacis[Amblyseius fallacis] [cf. next abstract], I. conspicuus, Seiulus bakeri and Amblyseius (Amblyseiopsis, subgen. n.) americanus, all of which are new species, and I. (Seiulus, Seius) pomi, Parrott. Notes are given on the characters and scope of some of the genera, and a new subfamily is erected for one of them.