352 PALEONTOLOGY OF NEW YORK. 



extremity ; the lower portion produced on each side as a strongly elevated 

 ridge, curving slightly inward on the sides, then outward on approaching 

 the anterior margin of the valve ; each branch recurving and passing back- 

 ward, parallel to the median axis, as far as the base of the cardinal process. 

 The symmetrical spaces thus formed are each divided transversely by a 

 somewhat lower vertical ridge. Between the inner muscular walls in the 

 median line is a low, rounded, longitudinal ridge. 



The surface is smooth or covered with concentric, usually somewhat squa- 

 mous lines of growth. 



Lower Helderberg group. Perry county, Tennessee. 



LEPTiENISCA ADNASCENS, Sp. nOV. 

 PLATK XVa, figs. 2i, 23. 



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 deltidium. Internal 

 characters as in L. 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). Near Clarksville, N. Y. 

 Lept^nisca tangens, sp. nov. 



PLATE XVa, FIGS. 21-30. 



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 ; del- 

 thyrium covered. In the pedicle-valve teeth not prominent but continued 

 into strong, converging lamellae which nearly enclose an oval muscular area ; 

 this area is divided by a median septum. External surface convex ; bi- 



