of 10 and 16
haemal arches were obtained in two of the specimens. Total height of
neural arches ranges from 7.5 to 12.0 mm., and of haemal arches, from
9.0 to 12.0 mm. The shorter arches are anterior and the height increases
gradually to a maximum in the caudal region. Height of the spines varies
from 4.0 to 9.0 mm., or from twice the height of the arch in the
anterior to three times the height in the caudal region. Total width of
the base, measured in isolated specimens because lateral views in other
specimens prevented measuring width, ranges from 0.7 to 4.2 mm. The
short, broad arches having short spines occur at the anterior end of the
spinal column; the narrower arches having tall spines occur toward the
caudal end. Broken neural and haemal arches show a thin covering of bone
with a central, calcite-filled cavity, which in life may have been
filled with cartilage (Stensioe, 1932:58, fig. 20).

No ossified ribs have been observed, either isolated or in place.

For further description of the axial skeleton, see Hibbard (1933).

[Illustration: FIG. 6. _Synaptotylus newelli_ (Hibbard). Paired fin
girdles. A, pectoral girdle, lateral view, based on K. U. no. 11433, x
3.5. B, pelvic girdle basal plate, medial (?) view, based on K. U. no.
788, x 8. Anterior is toward the left.]

_Girdles and paired fins_

A nearly complete pectoral girdle on specimen K. U. no. 11433 (see fig.
6A) has only a cleithrum and clavicle. No evidence of an extracleithrum
or supracleithrum has been observed, but the extracleithrum may be fused
to the cleithrum. The two bones form a boot-shaped unit, with the
anteroventral part turned medially to form a horizontal process which
meets the opposite half of the girdle. In lateral view the surface is
unornamented, and convex in the ventral half. The suture between the
cleithrum and clavicle begins on the expanded posterior portion, the
"boot-heel," at a point immediately below the greatest width on the
posterior margin, passes anteriorly, then turns sharply and parallels
the anterior margin. The shape of the cleithrum resembles that in
_Rhabdoderma_ and the internal surface is not ridged (see Moy-Thomas,
1937:fig. 9). The exact orientation in the fish is uncertain, but if the
median extension is really horizontal, then the posterior expansion is
directed caudally. The medial surface is concave, steepest near the
anterior margin, and then slopes outward evenly. In medial view one
specimen (K. U.