_a. com_, anterior commissure of lateral-line canals; _com_, commissural communication between infra- and supra-orbital lateral-line canals; _fr_, frontal; _inf_, interfrontal; _inn_, internasal; _info_, infraorbital lateral-line canal; _it_, intertemporal; _jl_, jugal lateral-line canal; _j_, jugal; _lar_, lacrimal; _mx_, maxilla; _n_, nasal; _oc_, occiput; _occ_, occipital cross-commissure of the lateral-line system; _or_, orbit; _par_, parietal; _pof_, postfrontal; _pmx_, premaxilla; _pf_, prefrontal; _po_, postorbital; _pp_, postparietal; _g_, quadrate; _qj_, quadratojugal; _spo_, supraorbital lateral-line canal; _sq_, squamosal; _spt_, supratemporal; _t_, temporal lateral-line canal; _tab_, tabulare.] (_a_) The skull of the Coal Measures Amphibia has (fig. 6) essentially the same structure in the different groups. It is largely formed of bones of intramembranous origin, representing the _face_ bones of the mammalian skull. The skull in life was doubtless a _chondrocranium_ with the membrane bones laid down upon the cartilaginous box containing the sense-organs, as in the sturgeon (_Acipenser_), where the surface bones of the face were probably originally scales, which later became consolidated into large bony scutes. The membrane bones of the early Amphibia may have been originally derived from scales, but at present nothing is known of this origin; doubtless the elements had an intramembranous origin in the ancestors of the group. Judging from Credner's studies on the series of specimens of _Branchiosaurus amblystomus_ Credner (187), the skull bones do not ossify completely until relatively late in the life of the individual. The skull in the youngest individual figured by Credner (_op. cit._, Taf. XVI, fig. 1) seems to be largely cartilaginous, with beginnings of separation into the skeletal elements. The manner and time of development and ossification of the skull seems to proceed much as it does in modern amphibians. The condition found in the skull of _Cryptobranchus allegheniensis_ or _Necturus maculosus_ will represent pretty accurately the condition of most of the Coal Measures Amphibia. The face bones in certain forms were sculptured and cut by lateral-line canals.