352 Report of the State Geologist. . 



The surface is smooth or covered with concentric, usually 

 somewhat squamous lines of growth. 



Lower Helderberg group. Perry county^ Tennessee. 



Leptaenisca adnascens. 



Plate 6, figs. 26, 27. 



Leptcenisea adnascens, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 

 352, pi. XV a, figs. 22, 23. 1892. 



Shell small, very irregular* in outline ; cemented to shells of 

 other brachiopods, especially of Orthis, by the entire external 

 surface of the pedicle-valve. Hinge-line making the greatest 

 diameter of the shell. Cardinal area well developed on the 

 pedicle- valve and bearing a convex deltidmm. luternal charac- 

 ters as in Z. tangens. Brachial valve prominent at the beak, 

 elevated in the umbonal region and slightly depressed anteriorly. 

 Surface smooth or with irregularly concentric wrinkles. 



Lower Helderberg group (Shaly limestone). Wear Clarhsville, 

 I^. Y, 



Leptaenisca tangens. 



Plate 6, figs. 19-25. 



Leptcenisea tangens, Hall. Palaeontology of N. Y., vol. VIII, pt. l,p. 352, pi. 

 XV a, figs. 24-30. 1892. 



Shell transverse; hinge-line making the greatest diameter; 

 contour regularly convexo-concave ; attached by the apical or 

 umbonal portion of the pedicle- valve, usually fronds and twigs of 

 bryozoa. Cardinal areas narrow ; delthyrium covered. In the 

 pedicle- valve teeth not prominent but continued into strong, con- 

 verging lamellae which nearly enclose an oval muscular area ; 

 this area is divided by a median septum. External surface con- 

 vex; bilobed by a more or less conspicuous median furrow. 

 Brachial valve strongly concave. 



Surface smooth, with a few inconspicuous concentric growth- 

 lines, and faint radiating striae on the inner lam ell a3 toward the 

 margins. 



Lower Helderberg group (Shaly limestone), l^ear Clarks- 

 mlle.N. Y. 



