. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 391 The orbits are completely surrounded by bone as a result of the fusion of the suborbital plates to the dorsal shield. The dentine ridges are very fine, with narrow crests and with lateral projections at their Fig. 131. Listraspis canadensis, type; incomplete dorsal shield exposed on inner side, National Museum of Canada 10030 (X 2). h, fossa for sixth gill pouch; Ibr, lateral brim; orb, channel leading to orbit, exposed by removal of ventral rostral lamina; pfo,
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 391 The orbits are completely surrounded by bone as a result of the fusion of the suborbital plates to the dorsal shield. The dentine ridges are very fine, with narrow crests and with lateral projections at their Fig. 131. Listraspis canadensis, type; incomplete dorsal shield exposed on inner side, National Museum of Canada 10030 (X 2). h, fossa for sixth gill pouch; Ibr, lateral brim; orb, channel leading to orbit, exposed by removal of ventral rostral lamina; pfo, fossa for pineal organ; ro, ros- trum; sec, depressions for semicircular canals. Listraspis canadensis, new species. Figures 131-133. Type.—National Museum of Canada, 10030, incomplete dorsal shield exhibiting the inner side (fig. 131). Referred specimens.—Incomplete dorsal shields, National Museum of Canada, 10031-10032 and CNHM, PF 3682-3685; ventral shields, National Museum of Canada, 10033, and CNHM, PF 3687-3693. Occurrence.—Early Devonian, about 30 miles northwest of Mun- cho Lake, British Columbia, 59° 07' 30" N., 126° 22' W. (locality R5-61, 2100' of California Standard Company). Diagnosis.—The length of the dorsal shield is 26-32 mm., its width ratio is usually ., its pineal ratio is .21-24, and its or- bital ratio is .13-. 15. The length of the ventral shield is 24-28 mm. On the dorsal shield there are 13-14, and on the ventral shield 8-10 dentine ridges per 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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