ely related to _Rhabdoderma_ than to the
Diplocercines because the anterior portion of the endocranium contains
only a basisphenoid, parasphenoid, and probably ethmoids. The
sphenethmoid region was certainly not a large, unpaired unit as in the
Diplocercines. Probably the posterior part, the otico-occipital region
(not known in _Synaptotylus_), was much more nearly like that of
_Rhabdoderma_, which consisted of unpaired basioccipital and
supraoccipital, and paired prootics, exoccipitals, and anterior and
posterior occipital ossifications (Moy-Thomas, 1937: figs. 3, 4).
Moy-Thomas (1937:389) points out that in _Rhabdoderma_ the occipital
region is "considerably more ossified" than in any coelacanths other
than the Devonian forms. Berg (1940:390) thought that the Carboniferous
coelacanths should be placed in a separate family because they did not
have two large, unpaired bones in the endocranium. _Rhabdoderma_ and
_Synaptotylus_ represent another stage in evolution of the endocranium
in coelacanths, and, if classification is to be based on endocranial
structure, then this stage (represented by the two genera) may later be
given family rank as Berg suggested. Because _Rhabdoderma_ and
_Synaptotylus_ have only part of the sphenethmoid region ossified and
because they retain basipterygoid processes, they are considered to be
related and are included in the subfamily Rhabdodermatinae.

~Synaptotylus~, new genus

_Type species._--_Synaptotylus newelli_ (Hibbard).

_Horizon._--Rock Lake shale member, Stanton formation,
Lansing group, Missouri series, Upper Pennsylvanian.

_Diagnosis._--Late Pennsylvanian fishes of small size, having the
following combination of characters: on basisphenoid, knoblike antotic
processes connected by a low ridge to basipterygoid processes; entire
ventral surface of parasphenoid toothed; anterior margin of parasphenoid
notched and no evidence of hypophyseal opening. Dermal bones of skull
smooth or with low, rounded tubercles and striae; fronto-ethmoid shield
incompletely known but having one pair of large rectangular frontals
with posterolaterally slanting anterior margins; intertemporals large,
the lateral margins curving laterally; postorbital triangular, apex
downward; subopercular somewhat triangular; squamosal carrying sensory
canal that curves down posteriorly and extends onto a ventral
projection; opercular generally triangular; supratemporals elongate,
curving to fit late