Palaeoemys testudiniformis was an early geoemydid freshwater turtle with a low oval shell strengthened by three longitudinal keels. The shell is noticeably angular in cross-section, suggesting a well-armoured aquatic turtle rather than a highly domed terrestrial form. Its occurrence in marine London Clay sediments is most readily explained by life in rivers, ponds or estuarine waters connected to the coast, with carcasses or shells sometimes reaching the sea.

Its diet has not been preserved directly. A mixed diet of aquatic invertebrates, plant material and other small food items is plausible for a geoemydid of this body form, but should remain an ecological inference. Most of what is known about the species comes from carapace and plastron anatomy, which preserves both its three-keeled body form and the arrangement of its shell scutes.