. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. 422 FIELDIANA: GEOLOGY, VOLUME 13 the posterior edge of the dorsal shield is produced into a rounded median lobe. There are about 7 dentine ridges per millimeter, and a broad, flat pineal macula is Fig. 144. Homalaspidella nitida, type (from Kiaer, 1932); dorsal shield, Paleon- tologisk Museum, Oslo, D 156 (X 3). orb, orbit. Discussion.—The diagnosis includes var. robusta (Kiaer and Heintz, 1935, p. 132), which differs from typical H. nitida only in its slightly larger size (length of dorsal
. The Cyathaspididae; a family of Silurian and Devonian jawless vertebrates. Cyathaspididae. 422 FIELDIANA: GEOLOGY, VOLUME 13 the posterior edge of the dorsal shield is produced into a rounded median lobe. There are about 7 dentine ridges per millimeter, and a broad, flat pineal macula is Fig. 144. Homalaspidella nitida, type (from Kiaer, 1932); dorsal shield, Paleon- tologisk Museum, Oslo, D 156 (X 3). orb, orbit. Discussion.—The diagnosis includes var. robusta (Kiaer and Heintz, 1935, p. 132), which differs from typical H. nitida only in its slightly larger size (length of dorsal shield=23-26 mm.) and broader proportions (width ratio= .54 as compared to . in typ- ical forms). Kiaer and Heintz (op. cit., p. 129) indicated that there are only 5 dentine ridges per millimeter, but measurements of their figures and a cast of the type show about 7. Their reconstruction of the dorsal lateral line pattern (fig. 98,D) shows that the dorsal trans- verse commissures were reduced, but that the longitudinal canals were continuous. In the ventral shield (fig. 99,C), the postoral canals continue into medial ventral canals, the latter appearing, anteriorly at least, as longitudinal canals rather than as transverse commissures. This species is not far removed from Poraspis, with which it is asso- ciated in the Spitsbergen deposits. Homalaspidella borealis Denison. Figures 145-147. Homalaspidella borealis Denison, 1963, Fieldiana: Geol., 14, no. 7, pp. 123-127, figs. 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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