. Bulletin - New York State Museum. Science. i8o NEW YORK STATE MUSEUM (1828. Genus leptaena Dalman [Ety.: Xerr-o^, thin] Kotigl. Svcnska Vet. Akad. Handl. p. 93,94) Shells concavo-convex; surface covered by conspicuous concen- tric corrugations or wrinkles over the flatter portions of the valves. Where these cease, the surface is more or less abruptly deflected, forming a conspicuous anterior slope. Whole exterior covered with fine, radiating, tubular striae, which in well preserved specimens are crenulated by finer concentric striae. Hinge line straight; cardinal area narrow. A convex deltid
. Bulletin - New York State Museum. Science. i8o NEW YORK STATE MUSEUM (1828. Genus leptaena Dalman [Ety.: Xerr-o^, thin] Kotigl. Svcnska Vet. Akad. Handl. p. 93,94) Shells concavo-convex; surface covered by conspicuous concen- tric corrugations or wrinkles over the flatter portions of the valves. Where these cease, the surface is more or less abruptly deflected, forming a conspicuous anterior slope. Whole exterior covered with fine, radiating, tubular striae, which in well preserved specimens are crenulated by finer concentric striae. Hinge line straight; cardinal area narrow. A convex deltidium present, perforated at the apex by a foramen, which often en- croaches on the apex of the valve. A trilobed cardinal process and well defined muscular impressions are present. Leptaena rliomboidalis (Wah- lenberg) (Fig. 84). Leptaena depressa Hall (1852. Pal. N. F. 2:257, pi. 53, fig. 6a-l.) Distinguishing characters. Cor- rugated part gently convex to slightly concave; abrupt anterior deflection; strong concentric cor- rugations and fine striae. Narrow hinge area. Found in the upper Clinton limestone, the Clinton lenses, and the lower Rochester shale up to and in the Bryozoa bed. Rarely above this. Also at Lockport and elsewhere (Hall).. Fig. 84 Leptaena rhomboidalis Genus stropheodonta Hall [Ety.: (TTpoif-q, bend; ddob<;, tooth] (1852. Pal. N. Y. 2:63. Hall & Clarke, 1892; Pal. N. Y. v. 8, pt I, p. 284) Shell normally concavo-convex; hinge line usually equal to or greater than the greatest width of the shell. Area of the pedicle valve higher than that of the brachial valve, both furnished with projecting denticulations, which interlock and form articulations. Muscular areas well marked and variously bounded. A strongly marked bifid cardinal process occurs in the brachial 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 perfect
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