. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. Fig. 135. Dikenaspis yukonensis, type; incomplete dorsal shield, Princeton 17088 (X 3). A, lateral view of left side; B, rostral view. bro, branchial opening; mrp, median rostral process; pbl, postbranchial lobe; pop, preorbital process. aspis differs from other Irregulareaspidinae in the presence of distinct epitega, indicated especially by the more or less transverse ridges of the rostral epitegum (fig. 134, rep), and the semi-elliptical arrange- ment of the anterior ridges of the combined central ep
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. Fig. 135. Dikenaspis yukonensis, type; incomplete dorsal shield, Princeton 17088 (X 3). A, lateral view of left side; B, rostral view. bro, branchial opening; mrp, median rostral process; pbl, postbranchial lobe; pop, preorbital process. aspis differs from other Irregulareaspidinae in the presence of distinct epitega, indicated especially by the more or less transverse ridges of the rostral epitegum (fig. 134, rep), and the semi-elliptical arrange- ment of the anterior ridges of the combined central epitegum and postrostral field (fig. 134). An unusual feature of the lateral line system, unknown in other Cyathaspididae, is the presence of two pairs of longitudinal sensory canals on the rostrum. It is conceiv- able that this is a result of the excessive branching of the sensory canals. However, it may be of more fundamental significance. Some pteraspids have, in addition to the supraorbital canals, a pair of small branches directly over the orbits (, Protopteraspis pri- maera, Kiaer, 1928, fig. 1). Traquairaspis pococki (White, 1946, fig. 40) also has two pairs of anterior sensory canals. Holmgren (1942, p. 12) has suggested that the canals immediately over the orbits may have been innervated by the profundus nerves, and if. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Denison, Robert H. (Robert Howland), 1911-1985; Chicago Natural History Museum. Chicago : Chicago Natural History Museum Press
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