. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 383 terminated quite abruptly anteriorly, that is, at the posterior borders of the branchial Fig. 124. Vernonaspis sekwiae, type; anterior part of dorsal shield, National Museum of Canada 10036 (X 5). cep, central epitegum; lep, lateral epitegum; orb, orbit; pm, pineal macula; rep, rostral epitegum; soc, pores of supraorbital sensory canal. Vernonaspis sekwiae new species. Figures 100,C, 123-124. Type.—National Museum of Canada 10036, dorsal shield, com- plete ant
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 383 terminated quite abruptly anteriorly, that is, at the posterior borders of the branchial Fig. 124. Vernonaspis sekwiae, type; anterior part of dorsal shield, National Museum of Canada 10036 (X 5). cep, central epitegum; lep, lateral epitegum; orb, orbit; pm, pineal macula; rep, rostral epitegum; soc, pores of supraorbital sensory canal. Vernonaspis sekwiae new species. Figures 100,C, 123-124. Type.—National Museum of Canada 10036, dorsal shield, com- plete anteriorly but preserved only as an internal impression in the posterior two-thirds (figs. 123-124). Referred specimens.—CNHM, PF 3673, crushed dorsal shield; PF3674, incomplete dorsal shield; PF 3675-3676, incomplete ven- tral shields; PF 3676-3678 and National Museum of Canada 10037, shield fragments. Occurrence.—Late Silurian, probably Late Ludlovian, top of Mt. Sekwi, beside Keele River, Northwest Territories, Canada; 63° 28' N; 128° 40'W. (California Standard Company locality Z-29-61; hori- zon 4994'-5080'). Diagnosis.—The dorsal shield has a length of about 33 mm., and ^Yr-^Yi dentine ridges per millimeter. Its posterior edge is nearly transverse, probably with little or no median lobe. Its width ratio is about .64. The orbital and pineal ratios are greater than in other species. Discussion.—This species is of about the same length as Vernon- aspis allenae but is relatively broader. Proportionate width is usually difficult to determine reliably, but two dorsal shields (National Mu- seum of Canada 10036 and PF 3674) are little flattened or distorted,. 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
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