"P. xinjiangensis" is distinguished by a prominent jugal 'horn' that is flattened on the front end, as well as some features of the teeth. The ilium, one of the three bones of the pelvis, also bears a characteristically long bony process behind the acetabulum (hip socket). An adult femur has a published length of about 16 centimetres (6.3 in). "P. meileyingensis" has the shortest snout and neck frill of any species, making the skull nearly circular in profile. The orbit (eye socket) is roughly triangular, and there is a prominent flange on the lower edge of the dentary, a feature also seen in specimens of "P. lujiatunensis", and to a lesser degree in "P. mongoliensis", "P. sattayaraki", and "P. sibiricus". The complete type skull, probably adult, is 13.7 centimetres (5.5 in) long. The dentary of "P. sattayaraki" has a flange similar to that found in "P. mongoliensis", "P. sibiricus", "P. lujiatunensis" and "P. meileyingensis", although it is less pronounced than in those species. The material appears to be roughly the same size as "P. sinensis". The frontal bone of "P. neimongoliensis" is distinctly narrow compared to that of other species, resulting in a narrower skull overall. The ischium bone of the pelvis is also longer than the femur, which differs from other species in which these bones are known. The type specimen has a skull length of 13.2 centimetres (5.2 in) and a femoral length of 13 centimetres (5.1 in), but is not fully grown. An adult "P. neimongoliensis" was probably smaller than "P. mongoliensis", with a proportionately longer skull and tail. "P. ordosensis" can be distinguished by numerous features of the jugals, which have very prominent 'horns'. It is also the smallest known species. One adult skull measures only 9.5 centimeters (3.75 in) in length.