Smithsonian Contributions to Knowledge (V. 8 1856)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1865 edition. Excerpt: ...of our shell are nearly equally convex; and that none of the descriptions we have read mention any difference in the distinctness of the radiating striae on the two valves, we would scarcely hesitate to refer the specimens now before us to M. substriata. Locality and position.--Southwest base Black Hills. Jurassic. (Type No. 205.) 11 September, 1884. Family TRIGONIIDE. (See page 57.) Genus TRIGONIA, Brugtjiere., Synon.--Trigonia, Broo. Encyc. Meth. I, 1789, xiv, pi. 237.--Lahk. Prodr. 1799, 86; Id. Syst. An. 1801, 116, and An. du Mus. IV, 1804, p. 351.--Roibby, Mol. VI, 1805, 392, &c. Lyrodon, G. B. Sowerbt, Genera Shells, 1833, faso. 41. Lirodon, Bhohn, Leth. 1837 (sec. ed.) 367 and 700. Lyriodon (part), Golbp. Petref. Germ. II, 1837, 196.--Bbonn, Jahrb. 1838, p. 108. Etym.--Tfiymcf, three cornered. Type.--Trigonia scabra, Lamk.. Shell subtrigonal, longitudinally ovate, elongate, or subcircular; postero-dorsal region often prodded with a more or less distinctly denned escutcheon or corselet. Surface ornamented with radiating, oblique, or concentric costae or rows of nodes; rarely smooth. Beaks usually elevated. Ligamdht short and prominent. Hinge thick, composed of two large diverging, elongate, transversely furrowed teeth, in the right valve, and three or four in the left, furrowed only on one side. Impressions of adductor muscles usually well defined, the anterior being located near the beaks. Scar of posterior pedal muscle located a little above, and in front of, the impression of the posterior adductor; antero-pedal scar generally placed within the cavity of the beaks, sometimes wanting in the right valve. Many of the extinct species generally referred to this genus differ so widely in form and surface ornamentation from each...