SUMMARY
A new genus of Pennsylvanian coelacanths, Synaptotylus, is described and a previously named species, Coelacanthus newelli Hibbard, 1933 (C. arcuatus Hibbard, 1933, is a junior synonym), is referred to this genus. All specimens of Synaptotylus newelli (Hibbard) were collected from the Rock Lake shale member of the Stanton formation, Lansing group, Missouri series, six miles northwest of Garnett, Anderson County, Kansas. Synaptotylus is distinguished from all other coelacanths by a basisphenoid having large, knoblike antotic processes each connected by a low ridge to a small basipterygoid process. Synaptotylus is most closely related to Rhabdoderma, but is intermediate between Rhabdoderma and Coelacanthus in shape of the fin girdles and basal plates. Two new subfamilies, Diplocercinae and Rhabdodermatinae, of the family Diplocercidae, are proposed. Synaptotylus and Rhabdoderma are included in the subfamily Rhabdodermatinae, because both exhibit reduced ossification in the endocranium and retain basipterygoid processes.
Loss of the basipterygoid processes in post-Carboniferous coelacanths may reflect the development of a more efficient feeding mechanism, by allowing the palatoquadrate complex and mandible to swing farther laterally and expand the oral cavity.
Synaptotylus newelli (Hibbard) may have occupied either the sea or fresh water; these fishes occur in lagoonal deposits with reptiles and amphibians, arthropods, marine invertebrates and remains of land plants.
Because scale patterns on Synaptotylus and Rhabdoderma are so nearly similar and vary with size of the scale and its location on the fish, it is recommended that isolated scales not be assigned to a species, and to a genus only with great caution.