. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 423. Fig. 145. Homalaspidella borealis, type (from Denison, 1963); dorsal shield incomplete posteriorly, Princeton 17101 (X 4). orb, orbit. Type.—Princeton 17101, a dorsal shield, incomplete posteriorly (figs. 145, 146,B). Referred specimens: Princeton 17092, 17102, 17378-17383. Occurrence.—Probably Early Devonian (Early Downtonian) lime- stones and graptolitic shales,1 Beaver River, southeastern Yukon. Diagnosis.—The length of the dorsal shield is 28-30 mm., and the orbital
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 423. Fig. 145. Homalaspidella borealis, type (from Denison, 1963); dorsal shield incomplete posteriorly, Princeton 17101 (X 4). orb, orbit. Type.—Princeton 17101, a dorsal shield, incomplete posteriorly (figs. 145, 146,B). Referred specimens: Princeton 17092, 17102, 17378-17383. Occurrence.—Probably Early Devonian (Early Downtonian) lime- stones and graptolitic shales,1 Beaver River, southeastern Yukon. Diagnosis.—The length of the dorsal shield is 28-30 mm., and the orbital ratio is .10-. 12. The rostral margin is nearly transverse, and the posterior edge of the shield is gently convex with no median lobe. There are dentine ridges per millimeter. A pineal macula is lacking. 1 Tentatively assigned to the Middle Ludlovian in Denison (1963); see below 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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