AbstractBased on a compatative study of the system of lateral line grooven on the paranmchal plate ofArctonemasp. from the Devonian of Spitsbergen and some of the holonematids and cocontents, the conclusion is reached that in these forms, one may have a pontiot “pit‐line” complex coresponding to that developing onlogenelically inPretoptenusamong the dipnoans. Observations on the lateral line system of various ptyctodontids include the following. In Chehophonus the lateral lines of the anterior part of the hend presumably possessed regularly spaced dilatation, resembling those of the corresponding lines in some recent holocephallane In cremurella, where also some new lateral line system components are put on record, the infraorbital canal was in front of the “marginal” plate enclosed in a bony tube, arisen by the fusion of ring‐like elements. In cremurella there is even reason to believe that ontogenetically, the component of the dermal bones formed as series of bony ring‐like elements, similar to they accompansing the lateral lines in fossil and recent holocephalians. In some forms as Chehophonus and Rhynchodus, a distinelly developed profundus lateral line has been identified. The holotype of “Lpipetalu” Gross is refigured and referred to n new ptyctodontid genus,