LINGULA 35 



LINGULA GORBYI Miller 

 Plate I, Figs. 1, 2 



1892. Lingula gorbyi Miller, Adv. Sheets 18th Rep. Geol. Surv. Ind., p 55. 



pi. 9, figs. 3, 4. 

 1894. Lingula gorbyi Miller, 18th Rep. Geol. Surv. Ind., p. 309, pi. 9, 



figs. 3-4. 



Description. Shell small, subelliptical in outline, the width more than 

 one-half the length. The dimensions of a nearly complete valve are: 

 length 11 mm., width 7.2 mm. 



Valves gently convex, the anterior margin subsemicircular, the lateral 

 margins gently convex, the postero-lateral margins nearly straight or 

 gently convex and meeting at the beak in a rounded, obtuse angle. 

 Surface marked by very fine, exceedingly regular, concentric costs, from 

 12 to 15 of which occupy the space of 1 mm., and usually by rather ob- 

 scure concentric undulations. 



Remarks. This species may be recognized by its exceedingly regular con- 

 centric costae. 



Horizon. Chouteau limestone of the Kinderhook. 



LINGULA HALLI White 



Plate I, Fig. 4 

 1862. Lingula Halli White, Proc. Boston Soc. Nat. Hist., vol. 9, p. 30. 



Description. Shell very small, longitudinally subelliptical in outline, 

 the length about twice the width, the greatest width a little in front 

 of the middle ; the postero-lateral margins meeting at the beak in an acute 

 angle, the lateral margins gently convex, the anterior margin narrowly 

 rounded. The dimensions of the holotype are : length 6.1 mm., greatest 

 width 2.8 mm., convexity of pedicle valve .8 mm. 



Pedicle valve rather strongly convex in proportion to the width, the 

 greatest convexity posterior to the middle ; the beak, in the internal cast, 

 rather abruptly constricted and produced posteriorly a little beyond the 

 general margin of the valve. Surface marked by fine, concentric lines 

 of growth, somewhat variable in strength. 



Brachial valve imperfectly preserved, its convexity evidently about 

 equaling that of the pedicle valve. 



Remarks. The holotype of this species is an internal cast of what is 

 probably the pedicle valve, preserved upon a fragment of white chert. 

 The reverse of the same chert fragment preserves small portions of the 

 shell substance of this valve and the incomplete brachial valve, somewhat 

 displaced, exhibiting the internal surface of its posterior portion. The 

 species differs notably from any of the other recognized Lingulas in the 

 faunas under consideration, in its narrowly subelliptical shell, approach- 



