Two long, narrow, splintlike bones covered on one surface with granular teeth are interpreted as ectopterygoids. These are 13.0 and 16.0 mm. long and each is 1.5 mm. wide. Orientation of these is unknown, but they probably fitted against the ventral surface of the ventral process of the endopterygoid (Moy-Thomas, 1937:fig. 5).
Fig. 5. Synaptotylus newelli (Hibbard). A, ceratohyal, lateral (?) view, based on K. U. nos. 11429 and 11457, × 5. B, urohyal, based on K. U. no. 11457, × 5.
The metapterygoid has a smooth surface in both views. The dorsal edge has a thickened, flared margin that presumably articulated with the antotic process of the basisphenoid. No articular surface for the basipterygoid process has been observed.
The quadrate is distinct and closely applied to the posteroventral margin of the complex. In medial view the margin is nearly straight and continues to the ventral edge. The ventral surface is thickened and forms a rounded, knoblike articular surface. In lateral view the surface is smooth; the anterior margin is irregular (or perhaps broken on all specimens), and proceeds in an irregular convex curve from the posterior to the ventral margin.
The general shape of the palatoquadrate complex is most nearly like that of Rhabdoderma elegans (Moy-Thomas, 1937:fig. 5). The orientation of the complex in the living fish was probably oblique, with the processus ascendens nearly vertical, the quadrate oblique, and the ventral process of the endopterygoid extending dorsoanteriorly and articulating with the parasphenoid.
Of the hyoid arch only the ceratohyals (see fig. 5A) are preserved in several specimens. These are long, curved bones with a posteroventral process and widened, flaring posterior margin. The medial (?) surface is concave in one specimen. The lateral (?) surface displays a distinct ridge on several specimens, arising on the dorsal surface opposite the posteroventral process and extending diagonally to the anteroventral end of the anterior limb. The impression of one other specimen appears to have a central ridge because of greater dorsal thickness and narrowness. Both surfaces are unornamented.
The urohyal (see fig. 5B) is an unornamented, Y-shaped bone, with the stem of the Y pointing anteriorly. Orientation with respect to dorsal and ventral surfaces is uncertain. In one view a faint ridge, also Y-shaped, occurs on the expanded posterior portion, and the surface is convex. The anterior process has a convex surface, sloping evenly off to the lateral margin; the opposite side of the process has a concave surface. The posterior portion has a slightly depressed area (see fig. 5B) at the junction of the "arms" of the Y.
The five branchial arches are represented by the ceratobranchials, several of which are preserved on K. U. no. 11431. These are long bones with anteriorly curving ventral ends. The medial surfaces are partly covered with minute granular teeth; only the dorsal part is without teeth. The dorsal articular surface is convex dorsally and rounded.
The mandible (fig. 3), the best specimens of which are K. U. nos. 788 and 11425, is seen only in lateral and ventral views, with only angular, splenial and dentary visible.