. Early Devonian fishes from Utah : Arthrodira. Fishes, Fossil; Paleontology -- Devonian; Paleontology -- Utah. DENISON: EARLY DEVONIAN FISHES 493 with certainty either to Aethaspis or to Simblaspis. Among the most interesting of these are dermal bones of the cheek, lower jaw, and perhaps upper jaw. Hitherto the only jaw elements known in Arc- tolepida were described in Phlyctaenaspis acadica (Heintz, 1933, pp. 132-133, pi. 2, figs. 2-4), but their preservation is not good. There are soc. Fig. 100. Bryantolepis sp. indet., restoration of anterior part of cranial roof based on PF 329 (X 3/2). P
. Early Devonian fishes from Utah : Arthrodira. Fishes, Fossil; Paleontology -- Devonian; Paleontology -- Utah. DENISON: EARLY DEVONIAN FISHES 493 with certainty either to Aethaspis or to Simblaspis. Among the most interesting of these are dermal bones of the cheek, lower jaw, and perhaps upper jaw. Hitherto the only jaw elements known in Arc- tolepida were described in Phlyctaenaspis acadica (Heintz, 1933, pp. 132-133, pi. 2, figs. 2-4), but their preservation is not good. There are soc. Fig. 100. Bryantolepis sp. indet., restoration of anterior part of cranial roof based on PF 329 (X 3/2). PI, pineal; PN, postnasal; PRO, preorbital; PTO, postorbital; RO, rostral; cc, central canal; ifc, infraorbital canal; soc, supraorbital canal. five rather well-preserved infragnathals in the collection from the Water Canyon Formation (PF 509-512, 984). The infragnathal is well known in many Brachythoraci. In Coccos- teus, which may be used as a typical form for comparison (Heintz, 1931, fig. 4; Watson, 1934, figs. 1, D, E; 2, D), it consists of a posterior blade and an anterior tooth-bearing part. In the Utah Arctolepida no blade is present, and the smooth, thin, posterior edge of the tooth- bearing part in PF 510 and 511 (fig. 101, B-D) shows that this is not caused by breakage. The probable implication of this is that the infragnathal of Brachythoraci is a compound bone with a separate center of ossification posteriorly. In Arctolepida the posterior dermal ossification may not have formed or may not have been discovered or recognized as a distinct element. The anterior, tooth-bearing part of the infragnathal of the Utah Arctolepida is similar in its general structure to that of Coccosteus. PF 509-511 (fig. 101, A-D), all of which may belong to the same species, illustrate the character of this bone well, especially PF 511, which has been prepared free of the rock. The bone is solid only along the dorsal, biting edge. Below this it consists of two nearly parallel, thin laminae
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