The cheek region is nearly complete in one specimen (K. U. no. 788), and scattered parts occur in a few others (see fig. 3). The lacrimojugal of no. 788 is elongate, with both ends curving dorsally. It differs from the lacrimojugal in R. elegans, in which the anterior end extends anteriorly and is not curved dorsally. The posterior and anterior margins are not preserved; the greatest height appears to be posterior. Pores of the suborbital portion of the infraorbital sensory canal are seen on the dorsal surface of the bone. In R. elegans the pores are on the lateral surface. A section of the lacrimojugal on specimen no. 11425, broken at both ends, shows a thin layer of bone perforated by the pores and covering a groove for the canal within the dorsal margin of the bone. Both specimens are unornamented.
A nearly complete postorbital (fig. 3) on specimen no. 788 is nearly triangular, with the apex ventral. The concave anterior margin bears pores of the postorbital part of the infraorbital line. Ornamentation consists of widely spaced, coarse tubercles.
Part of one squamosal is preserved. It is somewhat triangular and its apex is ventral. This bone is associated with the postorbital, subopercular and lacrimojugal on no. 788. The preopercular sensory line passes down the curving ventral margin of this bone, and extends ventrally onto a narrow projection. A low ridge, nearly vertical, passes dorsally from about mid-point of the canal to the dorsal portion. The anterior margin is nearly straight, the ventral margin is concave, and the dorsal margin is convex dorsally but may be incomplete. Perhaps the squamosal and preopercular are fused. The surface appears smooth; the view may be of the medial side. The squamosal of R. elegans is nearly triangular and notably different from that of Synaptotylus newelli.
The subopercular (fig. 3) shows closely spaced tubercles on the lateral surface. The bone is an elongated, irregular triangle with the apex pointing anterodorsally. The margins are incomplete, except for the concave, curving anterior margin.
Numerous operculars (fig. 3) occur in the suite of specimens, both isolated and nearly in place. Each is subtriangular; the apex of the triangle is ventral. A slight convexity projects from the anterodorsal border. The posterior margin is broadly but shallowly indented. Otherwise the margins are smooth. Maximum height ranges from 8.0 to 11.0 mm., and maximum width from 8.0 to 13.0 mm. Ornamentation varies from a few widely spaced, randomly oriented tubercles to closely spaced tubercles merging posteriorly into striae. On some specimens these are parallel to the dorsal border, and oblique in the central portion. On the posterior margins of several operculars the striae break up into tubercles. A few operculars have closely spaced tubercles over much of the surface. The internal surface is smooth.
Visceral skeleton
The palatoquadrate complex, best seen on K. U. no. 9939 (fig. 4), consists of endopterygoid, ectopterygoid, metapterygoid and quadrate. No trace of epipterygoids, dermopalatines or autopalatines, such as Moy-Thomas (1937:392, fig. 5) described for Rhabdoderma, has been observed.
The endopterygoid has a long, ventral, anteriorly-directed process, and an anterodorsal process that meets the metapterygoid in forming the processus ascendens. The suture between the endopterygoid and metapterygoid, seen in lateral view, is distinct in some specimens and has an associated ridge; these bones appear to be fused in others, without regard to size. This suture curves dorsally from a point anterior to the quadrate and passes anterodorsally to the extremity of the processus ascendens. The suture is visible on the medial side only near the processus ascendens, for it is covered by a dorsal, toothed extension of the endopterygoid. The endopterygoid has a smooth lateral surface; the medial surface is covered with tiny granular teeth, in characteristic "line and dot" arrangement. The teeth extend onto the ventral surface of the ventral process.
Fig. 4. Synaptotylus newelli (Hibbard). Restoration of the palatoquadrate complex, based on K. U. no. 9939, × 5. A, medial view, B, lateral view.