178 NEW YORK STATE MUSEUM 



free end, presents a surface for the attachment of the diductor, or 

 opening muscles, the opposite ends of which are attached near the 

 center of the pedicle valve, where they often leave pronounced scars. 

 A contraction of these muscles pulls on the cardinal process, and 

 draws the beak of the brachial valve toward the interior of the pedi- 

 cle valve, and thus opens the valves. Adductor muscles passing 

 from valve to valve and also commonly leaving scars, close the 

 valves again. Below the cardinal process and often merged with 

 it, is an elevated hinge plate whose surface often serves for muscu- 

 lar attachment. 



Beneath the beak of each valve frequently occurs a flat " cardinal 

 area ", bounded above by the cardinal slopes and below by the ar- 

 ticulating margin or hinge line. This area is commonly divided in 

 the center by a triangular fissure (dclthyrium) . It may be covered 

 either by a single plate (deltidium) or by two plates which join in 

 the center (dcltidial plates). 



The important surface features of the shell are : the lines of grozvth, 

 the radiating plications or striations, the fold or medial elevation, 

 and the sinus or medial depression, the fold commonly occurring on 

 the brachial, and the sinus on the pedicle valve. 



Genus lingula Bruguiere 



[Ety.: lingula, 'little tongue] 



(1789. Hist. nat. des vers tcstaccs; 1892. Pal. N. Y. v. 8, pt 1, p. 2) 



Shell with the valves nearly equal and varying in outline from 

 elongate ovate to subtriangular, always longer than wide; valves 



arched. Animal attached by a long 

 muscular pedicle which protrudes 

 from between the beaks of the two 

 i valves. 



Lingula cuneata Conrad (Fig. 81) 



. , (Hall. 1852. Pal. N. Y. 2:8, pi. 4) 



I Distinguishing characters. Acutely 



- ___ cuneate form; very acute beak with 



Fig. si Linguia cuneata enlarged x 2 nearly rectilinear margins; slightly 



curved base; valves convex near the beak, flatter toward front; fine 



longitudinal striae. 



Found in the upper Medina sandstones at Niagara. Also at 

 Lockport etc. (Hall). 



