. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. 378 FIELDIANA: GEOLOGY, VOLUME 13. VPrf Fig. 120. Vernonaspis bryanti, anterior part of type; dorsal shield, CNHM, PF838 (X 6). cep, central epitegum; lep, lateral epitegum; orb, orbit; pro, position of pineal macula, removed on this specimen; prf, postrostral field; rep, rostral epitegum. County, Pennsylvania (CNHM, PF 3646, collected by J. R. Beer- bower) . Diagnosis.—The length of the dorsal shield is 23-24 mm. Its dentine ridges are very fine, 8-9 per mm. The median lobe on the posterior edge of th
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. 378 FIELDIANA: GEOLOGY, VOLUME 13. VPrf Fig. 120. Vernonaspis bryanti, anterior part of type; dorsal shield, CNHM, PF838 (X 6). cep, central epitegum; lep, lateral epitegum; orb, orbit; pro, position of pineal macula, removed on this specimen; prf, postrostral field; rep, rostral epitegum. County, Pennsylvania (CNHM, PF 3646, collected by J. R. Beer- bower) . Diagnosis.—The length of the dorsal shield is 23-24 mm. Its dentine ridges are very fine, 8-9 per mm. The median lobe on the posterior edge of the dorsal shield is slight or absent. The width ratio is . Discussion.—Vernonaspis bryanti is the smallest species of the genus, and is distinguished from all except V. leonardi by its very fine dentine ridges. It may be identical to the species described by Flower and Way land-Smith as Archegonaspis drummondi, which agrees in its small size and fine ridges. However, as is indicated below (p. 444), the latter does not display characters permitting either generic or specific identification, so identity cannot be proved. The type dorsal shield is relatively broader than most other Ver- nonaspis, but the breadth may have been increased by crushing. The postbranchial lobe, well shown in the type and in PF 839, is relatively long (postbranchial ratio=.40) but is weakly developed. The ridge pattern is much as in V. vaningeni and V. allenae, that of the rostral epitegum and postrostral field being quite variable. In the rostral epitegum the central ridge pattern is elliptical in PF 838 (fig. 120), a pair of whorls in PF 839, fanned in Princeton 12922, and irregular and denticulate in New York State Mus. 9617; there. 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-
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