Fig. 2. Synaptotylus newelli (Hibbard). Restoration of the parasphenoid, based on K. U. nos. 9939, 11451, × 5. A, ventral view, B, dorsal view and cross sections.
The parasphenoid (see fig. 2) is a shovel-shaped bone having a wide anterior portion and a narrower posterior portion of nearly uniform width. Most of the ventral surface is covered with minute granular teeth. The anterior margin is flared and curved posteromedially from the lateral margin to a median triangular projection. The lateral margins curve smoothly from the greatest anterior width to the narrow central portion, where the margins become somewhat thickened and turned dorsally. Posterior to this the lateral margins are probably nearly straight. The external surface of the anterior section is nearly flat and has a central depressed area the sides of which slope evenly to the center. The internal surface is smooth and centrally convex. Because of the fragmentary nature of all four observed specimens, total length was not measured but is estimated to be 15 to 20 mm. The opening of the hypophyseal canal was not present, possibly because of crushing. Ethmoidal ossifications were not preserved in any of the specimens studied. The parasphenoid differs from that of Rhabdoderma elegans (Newberry) in being more flared and widened anteriorly and more concave centrally.
Dermal bones of the skull
Various portions of the cranial roof are preserved in several specimens (see fig. 3). For comparisons with Rhabdoderma elegans, see Moy-Thomas (1937:fig. 1).
The premaxillaries and rostral elements are not preserved in any of the specimens. Only one pair of relatively large frontals have been observed; they are 5.5 to 9.0 mm. long and 2.0 to 3.5 mm. wide. These are nearly flat bones, with the greatest width posteriorly 0.1 to 1.0 mm. wider than the anterior portion. The midline suture is straight, the lateral margins are nearly straight, the anterior margin slopes evenly posterolaterally, and the posterior margin is slightly convex to straight. The anterior margin in R. elegans is essentially straight. Ornamentation consists of sparse, unevenly spaced, coarse tubercles or short striae. In one specimen both bones have small clusters of tubercles near the lateral margins and about 2.0 mm. from the posterior margin. None of these bones has alisphenoids or ridges on the ventral surface, as Stensiö (1921:65, 97) described for Wimania and Axelia.
Fig. 3. Synaptotylus newelli (Hibbard). Diagram of the dermal bones of the skull, in lateral view, based on K. U. nos. 788 and 11432. × 2-1/2 approximately.
Only six supraorbitals have been preserved (see fig. 3). These are nearly square, flat, thin bones lying nearly in place adjacent to a frontal on K. U. no. 788. The smallest is anterior; the margins of all are nearly straight. The bones are unornamented. Each bears a pore of the supraorbital line just below the midline. The supraorbitals of R. elegans have a triangular outline and do not bear pores.
Intertemporals (fig. 3) on several specimens vary from approximately 9.0 to 15.0 mm. in length, 2.0 to 2.7 mm. in anterior width, and increase to 4.5 to 8.0 mm. in maximum posterior width. The midline suture is straight, the anterior margin is concave and the lateral margin proceeds laterally in a concave curve to the widest portion. In R. elegans only the anterior half of the corresponding margin is concave. The posterior margin is slightly rounded and slopes anteriorly toward the lateral margin. Ornamentation is usually of randomly oriented tubercles and striae, although striae are more common in the posterior third and may be longitudinal, whereas tubercles occur mainly on the anterior section. No evidence of sensory pores, as seen on the intertemporal of R. elegans, has been found.
The supratemporals were observed on only one specimen (K. U. no. 788), (fig. 3). Sutures were difficult to distinguish but the medial margin is presumed to curve to fit and to articulate with the lateral margins of the intertemporals. Lateral margins are smoothly curved but the anterior and posterior margins were broken off. There appears to be no ornamentation on this bone. The supratemporals are much more elongated and curving than those in R. elegans.