. Carnegie Institution of Washington publication. Figs. 113 and 114.—"Vertebral columns" ot "Silurian Chimaeroid," Dictyorhabdus priscus Walcott. The first figure after Walcott. ', oblique lamiDae in (he structure of the fossil, suggesting lines of Fig. 115.—Dental plates ot Men- aspis armata -^ Chalcodus (permi- anus). Kupferschiefer. After spec- imen in Berlin Museum. DEVONIAN CHIM/EROIDS. Chimreroid remains, or, more accurately, what are generally accepted as such, are widelj' distributed throughout the middle and especially the upper Devonian rocks of northern
. Carnegie Institution of Washington publication. Figs. 113 and 114.—"Vertebral columns" ot "Silurian Chimaeroid," Dictyorhabdus priscus Walcott. The first figure after Walcott. ', oblique lamiDae in (he structure of the fossil, suggesting lines of Fig. 115.—Dental plates ot Men- aspis armata -^ Chalcodus (permi- anus). Kupferschiefer. After spec- imen in Berlin Museum. DEVONIAN CHIM/EROIDS. Chimreroid remains, or, more accurately, what are generally accepted as such, are widelj' distributed throughout the middle and especially the upper Devonian rocks of northern Europe and North America. These are referred to the family Ptyctodontidae. Unfortunately for accurate diagnosis the fossils are fragmentary and the best results which can be obtained from them are brieflj' these: That in the three genera—all at present known—Ptyctodus, Rhynchodus, and Palseomylus, dental plates were present which resemble closely those of Chimaeroids. On the other hand, these plates were only four in number and their tritoral characters are puzzling. Within the substance of the plate appear not a few tubercular tritors, but a general series of tritoral points, sometimes arranged in lamella, which in turn maj' form a series of flat or curving surfaces tritoral in function. The tritoral points are most conspicuous in Ptyctodus (fig. ii6), where they form lamellae. In Paheomylus (fig. 117) they spread out diffusely, and in Rhynchodus (fig. 118) are drawn together close to the rim of the plates, forming thus an extended sectorial *The cephalopod nature of Dictyorhabdus was early commented upon by Hyatt, a reference which I had over- looked and for which I am recently indebted to my friend, Dr. C. R. 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 Carnegie Institution of Washing
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