Fig. 17. The interior of a brachial valve, showing the bilobed cardinal process 

 and the quadruple adductor scar, divided by high, vertical muscular 

 walls . 



Fig. 18. Cardinal view of the brachial valve, showing the cardinal process, 

 widely divergent crural plates, and the prominent longitudinal and trans- 



verse muscular ridges inclosing the scars of the adductor muscles, x 3. 



Lept^nisca tangens, Hall. 

 Page 352. 



Figs. 19, 20. Opposite sides of a pedicle-valve which has been attached to a 



frond of Fenestella. x 8. 



I 



Fig. 21. The exterior of a pedicle-valve in which the rugose growth has | 



obscured the median sinus . The deep umbonal cicatrix has been caused 

 by attachment to some bryozoan , x 3. | 



Figs. 22, 23 . Exterior and interior of a pedicle-valve, showing the cicatrix of | 



attachment, deltidium and dental plates, x 3. j 



Figs. 24, 25. Opposite sides of a pedicle-valve attached to a twig of Tremato- | 



pora. X 3. j 



Lower Helderberg group. Near Clarksville, N. Y. i 



Lept^nisca adnascens, Hall. 

 Page 352. 

 Fig. 26. A pedicle-valve attached by nearly its entire surface to the interior of 

 a valve of Orthis ohlata. The specimen shows the dental lamellae and 

 median ridge dividing the muscular area, x 3. 



Fig. 27. A specimen retaining both valves, attached to the surface of Orthis 

 perelegans. x 4. 

 Lower Helderberg group. Near Clarksville, N. Y. 

 49 385 



