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The skull of a lower actinopterygian bony fish (in these cases a paleoniscoid fish) is composed of several separate structural and functional units.

1. The skull roof is the dorsal surface of the neurocranium, alias the braincase, a solid unit that protects the brain and the special senses (sight, smell, hearing; A). The only other part of the neurocranium usually seen in a fossil fish is its midventral bone, the parasphenoid, where it passes through the orbit.
2. The external surface of the side of the head consists of bones of the snout, the cheek, and the lower jaw. The bones of the cheek are attached firmly to the underlying palate+hyomandibular, which is movably hinged to the neurocranium dorsally, to the opercular series of bones posteriorly, and to the lower jaw ventrally.  The bones of the snout are usually sutured to the neurocranium.
3. The opercular series of bones continues from the posterior surface of the head ventrally and anteriorly between the lower jaws. It is movably hinged to the hyoid visceral arch and serves as an important part of the respiratory/feeding pump.
4. The shoulder girdle is flexibly attached to the posterolateral end of the braincase and extends downward to meet its opposite side at the ventral midline. The shoulder girdle forms the framework interfacing the body to the head and the branchial/visceral elements.
5. The many bones of the branchial (gill) arches are very rarely seen intact or undisturbed. They support the gills, the respiratory organs.
6. The lateral line is a system of sensory canals that receive boundary layer water flow information from the interface between the fish and the water surrounding it. The lateral line system also fundamentally determines the centers of origin of the skull bones. Far more evolutionarily conservative than the bones themselves, the pathways of the canals and their sense organs through the bones are the principle determinants of bone homologies. Thus, for instance, the rostral bone is identified as the (small anterior) median bone carrying the ethmoid lateral line commissure across the snout, and the postrostral bone as the anamestic (non-canal-bearing) median bone posterior to it. If there is only one large median bone, with the canal near it's anterior edge, it is thus considered the fusion of rostral and postrostral, and called rostro-postrostral.

There are almost as many names for some of the skull bones as there are (and were) specialists to study them and argue about their homologies. The following names are topographic and traditional for paleoniscoids. However, different paleoniscoids have different numbers, shapes, and proportions of the bones, and some bones may fuse together.

The bones and lateral lines of a generalized lower actinoptygian skull are shown below right. A dorsal view of the skull roof is at the top and the lateral view of external skull bones is at the bottom.

Bones (in red, capital and lower case) Ae- anteopoerculars (accessory operculars) Aex- anterior extrascapulars An- angular Ao- antorbital B- branchiostegals C- cleithrum Cl- clavicle D- dentary Dh- dermohyal Dp- dermopterotic E- extralateral gular Ex- extrascapulars F- frontal Io- infraorbital Lg- lateral gular Lx- lateral extrascapular M- maxilla Mfm- maxillary fossa of mandible Mg- median gular Mx- median extrascapular N- nasal O- opercular P- parietal Pc- postcleithrum Pm- premaxilla Po- preoperculum Pr- postrostral Ps- presupracleithrum Pt- posttemporal R- rostral S- suborbitals Sc- supracleithrum Sl- sclerotics So- subopercular

Lateral Line Canals (in blue, lower case) ec- ethmoid commissure gu- gular pit line ic- infraorbital canal jq- jugal & quadratojugal pit-lines mc- mandibular canal ot- otic canal poc- preopercular canal pr- profundus canal soc- supraorbital canal stc- supratemporal commissure amp- anterior, median, & posterior parietal sensory pit lines