The family Penthaleidae consists of 6 genera (Chromotydaeus, Halotydeus, Linopenthaleus, Linopenthaloides, Penthaleus, Turanopenthalodes) with up to 45 more or less identifiable species. Some species in Halotydeus and Penthaleus are important plant pests. Banks described Penthaleus dorsalis as Notophallus dorsalis in 1902 from specimens collected in the early spring from under stones and sticks in Washington, D.C., USA. In 1946 Baker considered P. dorsalis a synonym of P. major. The last specimens of P. dorsalis from Washington D.C. were recorded in 1911 on winter crops planted in what today is known as the National Mall. This species was not recorded again until 2012 when farmers in eastern Maryland reported mite problems on winter and early spring Brassicaceae crops. Examination of the specimens revealed the mite to be P. dorsalis. To determine the range of P. dorsalis farms with winter and early spring crops in Maryland and nearby states were surveyed. Specimens of P. dorsalis were collected in Maryland, USA for laboratory study. Some specimens were mounted on standard microscope slides in Hoyer’s mounting media for examination on a light microscope. Live mites were photographed. Additional specimens were frozen in liquid Nitrogen for morphological examination in a Low Temperature Scanning Microscope (LTSEM). The survey of farms revealed P. dorsalis to be widespread in the states of Delaware, Virginia, West Virginia, Pennsylvania and Maryland, USA. Penthaleus dorsalis continues to be a pest of winter crops especially in field green houses in this region. Penthaleus mites are soft bodied and can be difficult to study from slide mounted specimens. The morphological examination of P. dorsalis using the LTSEM revealed new details of the chelicerae, opisthosomal chaetotaxy, leg chaetotaxy, and palps that could not be observed under light microscopy. In the laboratory live P. dorsalis had a high tolerance to cold and some were active at temperatures down to -25° C.