. Appendix to the Manual of Mollusca of Woodward, : containing such recent and fossil shells as are not mentioned in the second edition of that work . ich in some spe-cies bear prolonged calcined processes for the support of thecirrated arms. A more or less developed area in the ventral valve. In S. losvis and S. microcamerus the hinge line is straight andmuch extended. In S. Arachne, Billings, the area of the ven-tral valve is so much developed as to give the whole shell theexternal appearance of an Orthis. Distribution, 10 species. Middle Silurian, Europe, elongata, Va
. Appendix to the Manual of Mollusca of Woodward, : containing such recent and fossil shells as are not mentioned in the second edition of that work . ich in some spe-cies bear prolonged calcined processes for the support of thecirrated arms. A more or less developed area in the ventral valve. In S. losvis and S. microcamerus the hinge line is straight andmuch extended. In S. Arachne, Billings, the area of the ven-tral valve is so much developed as to give the whole shell theexternal appearance of an Orthis. Distribution, 10 species. Middle Silurian, Europe, elongata, Vanuxem, is the only species known in the Devonianrocks. Family IV. — Orthhle.* Skenidium, Hall, 1861. Etymology, skenidion, a little tent. Type, Orthis insignis. Shell having the general aspect of Orthis, except in the ex-treme elevation of the ventral valve ; cardinal process prolongedinto a median septum, which extends to the base or front mar-gin of the shell, and occasionally bifurcates at this lower ex-tremity. Area large and triangular in the typical species. Distribution, 3 species. Silurian, United States. Streptorhynchus, King, 1850 (see p. 380)..
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