Trionyx triunguisa (African or Nile softshell turtle, Forsskål 1775) extant. This taxon is a sister to Odontochelys of the Late Triassic. The genus Trionyx extends to the Cretaceous. The most striking feature of Trionyx triunguis, along with other soft-shelled turtles, is the flattened, skin-covered carapace lacking horny scutes. The skull of these turtles is also very distinctive, however, in being relatively very elongate and narrow

Trionyx triunguis skull in four views from Digimorph.org. Note the reduction of the squamosal between the jugal and quadrate, and the quadratojugal above the quadrate.

Ocepechelon bouyai (Bardet et al. 2013 Latest Cretaceous, OCP DEK/GE 516) was considered a suction feeding sea turtle. Not a chelonid, as originally described, Ocepechelon is a giant soft-shelled turtle, nesting with Trionyx. It is known from a single skull without mandibles. What was originally considered a dorsal narial opening is instead just a new opening of unknown use. The bones are relabeled here in accord with Trionyx.

Perochelys lamadongensis  (Li et al. 2015; Brinkman et al. 2017) is an Early Cretaceous soft-shell turtle close to and little different from Trionyx. The carapace has tiny beads. The tip of the rostrum is missing.

Bardet N, Jalil N-E, de Lapparent de Broin F, Germain D, Lambert O, et al. 2013. A Giant Chelonioid Turtle from the Late Cretaceous of Morocco with a Suction Feeding Apparatus Unique among Tetrapods. PLoS ONE 8(7): e63586. doi:10.1371/journal.pone.0063586

Gaffney ES 1975. A phylogeny and classification of higher categories of turtles. Bulletin of the American Museum of Natural History 155:387-436.

Li L, Joyce WG and Liu J 2015. The first soft-shelled turtle from the Jehol Biota of China. Journal of Vertebrate Paleontology 35(2):e909450. 2015

Brinkman D, Rabi M and Zhao L-J 2017. Lower Cretaceous fossils from China shed light on the ancestral body plan of crown softshell turtles (Trionychidae, Cryptodira). Scientific Reports 2017(7):6719.

Meylan PA 1987. The phylogenetic relationships of the soft-shelled turtles (family Trionychidae). Bulletin of the American Museum of Natural History 186:1-101.

wiki/Trionyx
digimorph.org/Trionyx