. Bulletin of the Buffalo Society of Natural Sciences. Natural history; Science. NIAGARA FALLS AND VICINITY 183 subauriculate; cardinal areas narrow, sometimes obscurely crenu- lated on the margins. Delthyrium partially closed by convex plate, but mostly occupied by cardinal process of opposite valve. Car- dinal process appears trilobate. Muscular areas moderately well defined. Plectambonites sericea (Sowerby) (Fig. 89). Leptaena s e r i c e a Hall (1852. Pal. N. Y. 2:59, pi. 21) 1 > -\ ' 'â .â ' Distinguishing characters. Outline â , ,\v \\ semicircular to semioval; hinge line ex- tended,
. Bulletin of the Buffalo Society of Natural Sciences. Natural history; Science. NIAGARA FALLS AND VICINITY 183 subauriculate; cardinal areas narrow, sometimes obscurely crenu- lated on the margins. Delthyrium partially closed by convex plate, but mostly occupied by cardinal process of opposite valve. Car- dinal process appears trilobate. Muscular areas moderately well defined. Plectambonites sericea (Sowerby) (Fig. 89). Leptaena s e r i c e a Hall (1852. Pal. N. Y. 2:59, pi. 21) 1 > -\ ' 'â .â ' Distinguishing characters. Outline â , ,\v \\ semicircular to semioval; hinge line ex- tended, ending in acute points; Striae Fig. 89 Plectambonites set icea strong, elevated, alternating with finer ones. Found in the lower Clinton limestone at Niagara. Rare. Plectambonites transversalis (Wahlenberg) (Fig. 90). Lep- taena trans versalis Hall (1852. Pal. N. Y. 2 \2.^o, pi. 53; fig- 5a-b) Distinguishing characters. Out- line semicircular; strongly convex pedicle, and extremely concave bra- chial valve, conforming to each other; strongly incurved beak of pedicle valve, which causes an inflection of the hinge line; hinge line produced; Fig. 90 Plectambonites transversalis - ,. , , . . fine distant elevated striae with ex- tremely fine striae between; strongly punctate character of ex- foliated portions. Found in the Clinton lenses, and abundantly in the lower Roches- ter shale at Niagara. Also at Lockport (Hall). Genus orthothetes Fischer de Waldheim [Ety.: 6pd6$; straight] (1830. Soc. imp. natural, d. Moscow Bui. 1:375. Hall & Clarke, 1892; Pal. N. Y. v. 8, pt 1, p. 253) Shell varying from plano-convex to biconvex, sometimes becom- ing concavo-convex with age. Pedicle valve most convex about the beak, which often tends toward irregular growth; cardinal area well developed, with a thick, more or less convex deltidium. Teeth not supported by dental plates. Brachial valve most convex near. Please note that these images are extracted from scanned page images that may hav
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