Welle7' — Kinderhook Faunal Studies. 445 



lacking. The elevation of the fold of the brachial valve is 

 another variable character, in some individuals it being quite 

 strongly elevated at the anterior margin of the shell while in 

 others it is not conspicuously elevated. 



The species is quite distinct from any of the recognized 

 species of the Kinderhook faunas, neither is it closely allied 

 to any of the later Devonian forms . 



Delthyris MISS0URIEN8IS n. sp. 



Plate 1; Jigs. 23-26. 



Description. Shell small, wider than long, the hinge-line 

 usually a little shorter than the greatest width. Pedicle 

 valve strongly convex, with a medium septum internally, the 

 umbo prominent, beak a little incurved ; the cardin irea 

 of moderate height, concave, delthyrium narrowly triangular; 

 lateral slopes convex antero-laterally, the slopes from the 

 umbo to the cardinal extremities sometimes slightly concave, 

 the cardinal margins angular ; sinus well defined to the beak, 

 rather shallow, rounded or somewhat flattened in the bottom. 

 Brachial valve regularly convex except towards the cardinal 

 extremities where it is more or less compressed ; fold sharply 

 defined, not greatly elevated abore the general surface of 

 the valve. Each valve marked by three or four strong, 

 rounded plications upon each lateral slope, becoming success- 

 ively smaller in passing towards the cardinal extremities; 

 surface of each valve also marked by strong crowded lamel- 

 lose lines of growth. 



The dimensions of a large pedicle valve are : length from 

 beak to front margin 10 mm., width 12.5 mm., convexity at 

 umbo 5 mm.; the dimensions of a large brachial valve are: 

 length 8.5 mm., width 13 mm., convexity 3.7 mm. 



Remarks. Most of the specimens of this species are con- 

 siderably smaller than the dimensions given above, the width 

 of a large number of individuals being less than 5 mm. The 

 brachial valves are much more commonly preserved than 

 the pedicle valves. 



These shells have the general aspect of several species from 

 the lower Misissippian faunas commonly referred to the 



