. The Canadian journal of industry, science and art. . Fig. 57. Pig. 56. Fig. ^Side view. Fig. 57.—Dofsal view of a specimen with a truncated front margin. Description.—-Transversely sub-oval; greatest width about the middle or a little above; the front margin sometimes extended into a short, broadly-rounded linguiform projection, and sometimes nearly straight, or even a little concave for about one-third the width. Both valves moderately convex; the ventral valve usually with a shallow mesial sinus, or depression, which becomes obsolete before reaching the beak ; dorsal valve with a broad
. The Canadian journal of industry, science and art. . Fig. 57. Pig. 56. Fig. ^Side view. Fig. 57.—Dofsal view of a specimen with a truncated front margin. Description.—-Transversely sub-oval; greatest width about the middle or a little above; the front margin sometimes extended into a short, broadly-rounded linguiform projection, and sometimes nearly straight, or even a little concave for about one-third the width. Both valves moderately convex; the ventral valve usually with a shallow mesial sinus, or depression, which becomes obsolete before reaching the beak ; dorsal valve with a broad slightly elevated mesial fold. Beak and umbo of ventral valve of moderate size, the former incurved, and perforated at the point by a circular aperture. The umbo of the dorsal valve is small and neatly rounded, the beak buried beneath that of the opposite valve. Surface marked by sharp concentric ridges, which are sometimes so greatly developed as to cover the whole shell with thin overlapping scale-like plates. Length from nine to fifteen lines; width a little greater than the length. This well known fossil has a very wide geographical distribution, being found in the Devonian rocks of Russia, Germany, France, Spain, England, and America. It varies a good deal in form, according to the sediment in which it is found. Where the shell is thin, the middle of the front margin is straight or concave, as in Fig. 57 ; but the thick-shelled indi- viduals have the front margin more or less pointed. Some think our species different from the European form ; but others, such as De Verneuil, Eoemer, Lyell, Sharpe, and others, who have compared specimens from both sides of the Atlantic, have pronounced them to be identical. Locality and ^OccviYS in the Corniferous Limestone in the Township of Cayuga, and in the Hamilton Shales at various places in the Township of Bosanquet. Collectors.—A. Murray, T. Richardsoti, J. De Please note that these images are extracted from s
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