omic significance at this level. Higher
categories should have as their basis characters that display
evolutionary sequences. A recent classification (Berg, 1940), followed
in this paper, reflects two evolutionary trends in endocranial structure
of coelacanths: reduction of endocranial ossification and loss of the
basipterygoid processes. Because there has been little change in other
structures in coelacanths, Berg's classification is the most useful.
Berg (1940:390) includes _Rhabdoderma_ in the suborder Diplocercidoidei
because of the presence of the basipterygoid processes, and in the
single family, Diplocercidae, but remarks that because of the reduced
amount of endocranial ossification the Carboniferous Diplocercidae
"probably constitute a distinct family." In considering this concept of
classification, the subfamilies Diplocercinae and Rhabdodermatinae of
the family Diplocercidae are proposed above. The subfamily
Rhabdodermatinae includes at present _Rhabdoderma_ and _Synaptotylus_.
The principal characters of the subfamily Rhabdodermatinae, named for
the first known genus, are the retention of the basipterygoid processes
and the reduction of endocranial ossification. Application of this
classification based upon endocranial structure would probably change
existing groupings of species of Carboniferous coelacanths; the entire
complex of Carboniferous genera should be redescribed and redefined. It
will be necessary to consider endocranial structure in any future
classification.

The greater part of the evolution previously mentioned appears to have
been accomplished during the Carboniferous; thereafter coelacanth
structure became stabilized. The trend progressed from Devonian
coelacanths which had two large unpaired bones in the endocranium, and
both antotic and basipterygoid processes on the basisphenoid, to
Carboniferous fishes in which ossification was reduced to a number of
paired and unpaired bones embedded in cartilage, and retaining both
processes, and then post-Carboniferous kinds with reduced ossification
and no basipterygoid processes. The Pennsylvanian was evidently the time
of greatest change for the coelacanths, and they have not changed
significantly since, in spite of the fact that since the Jurassic they
have shifted their environment from shallow, fresh water to moderate
depth in the sea (Schaeffer, 1953:fig. 1). The changes in endocranial
structure appear to be significant, and are perhaps related