BRACHIOPODA—PROTREMATA. 2 1 3 



A. Shell with radiating plications 83. S. costata. 



B. Shell with radiating striae *. 



* Shell nearly flat (1). 



(1) Surface with prominent concentric wrinkles 75. S. beckei. 



(1) Surface with only oblique folds at the hinge margin... 72. S. corrugata. 



(1) Surface with very slight concentric wrinkles or none a. 



a. Shell very thin. Striae usually wavy 85. 6". perplana. 



a. Shell thin. Striae straight 74. S. varistriata. 



* Shell quite concavo-convex (2). 



(2) Shell large (about \ x / 2 inches long or longer) b. 



b. Hinge extremities rounded 76. S magnified. 



b. Hinge line usually extended f. 



f Strong concentric striae present, crossing the finer striae. 



78. S. patersoni. 



f Strong concentric striae absent %. 



\ Shell conspicuously concavo-convex x. 



x Pedicle valve with greatest convexity near the front, aa. 



aa. Striae alternating 81. S. concava. 



aa. Striae not alternating 80. S. hemispherica. 



x. Pedicle valve with greatest convexity in the umbonal re- 

 gion 77. S. magnivenler. 



x. Pedicle valve regularly convex from beak to front. 



73. S. profunda. 



\ Shell slightly convex to flat 74. S. varistriata. 



(2) Shell small (about I inch long) c. 



c. Radiating striae strongest near the beak 84. S. demissa. 



c. Radiating striae not strongest near the beak 79. S. inequiradiata. 



(2) Shell very small (about )/ z inch long) d. 



d. Hinge line extended 82. S. inequistriata. 



d. Hinge line less than greatest width of shell 86. S. arcuata. 



72. r S. # corrugata (Conrad.) (Fig. 253.) Siluric. 



Small, nearly flat ; hinge line extended. Surface covered with 

 fine prominent striae. Oblique folds present on the hinge margin. 



Clinton of New York, Tennessee. 



Fig. 253. Stropheodonta corrugata, with surface enlarged. 



73. S. profunda Hall. (Fig. 254.) Siluric. 



Large, with width much greater than the length. Brachial valve 

 very concave with abruptly deflected margins. Surface covered 

 with fine unequal striae. 



