. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 461. Fig. 160. Americaspis americana; ventral shield, CNHM, PF 3308 (X 3/2), showing anomalous growth line (gl); photograph is of rubber impression of nat- ural mold. tral shield had become the main structural and growth units of the armor, and could have been formed only after growth had been com- pleted. This is confirmed by a thin section of Allocryptaspis lati- costata (fig. 159,B); though this specimen (CNHM, PF 3737) is of adult dimensions, its dorsal shield consists o
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. DENISON: THE CYATHASPIDIDAE 461. Fig. 160. Americaspis americana; ventral shield, CNHM, PF 3308 (X 3/2), showing anomalous growth line (gl); photograph is of rubber impression of nat- ural mold. tral shield had become the main structural and growth units of the armor, and could have been formed only after growth had been com- pleted. This is confirmed by a thin section of Allocryptaspis lati- costata (fig. 159,B); though this specimen (CNHM, PF 3737) is of adult dimensions, its dorsal shield consists only of a very thin layer of dentine capping the ridges and continuing into a thin layer of aspidine surrounding the intercostal grooves. These thin layers are the earliest stage in the formation of the exoskeleton, and appear to have formed over the whole dorsal shield at once. The formation of the shield differs from that of the Cyathaspidinae only in that the superficial parts of the dorsal shield probably form as a unit rather than as separate 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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