74 BBAOHIOPOUS. 



sinuous on its inner edge, for the reception of the cardinal 

 process of the other valve. Interior showing hinge teeth to 

 be well developed, trigonal, and striated on their posterior 

 sides ; while from their inner bases the dental laminae extend 

 forward so as nearly to encircle the usual saucer-shape depres- 

 sion for the muscular scars, which is sometimes divided by a 

 small, linear mesial ridge ; cardinal margin prominent and sharp 

 within on each side of the hinge teeth; anterior and lateral 

 regions more or less thickened within, and roughened by the 

 crossing of the vascular markings, which are scarcely visible 

 on any part within this zone. 



Surface of both valves ornamented by numerous fine, 

 closely crowded, radiating striae, that are often alternately a 

 little larger and smaller, or on some parts, with several of the 

 smaller ones between each two of the larger the smaller be- 

 ing always shorter than the larger, or ending at various dis- 

 tances between the free margins and the beaks, without coalesc- 

 ing with those between which they are intercalated. Striae and 

 furrows minutely crenulated by extremely small, very regular, 

 closely arranged concentric lines, invisible without the aid of 

 a magnifier; a few subimbricating marks of growth are like- 

 wise sometimes near the free margins. ( Meek.) 



Horizon art d localities Lower Silurian, Hudson shales: 

 Louisiana, Cape Girardeau. 



Strophodonta? cymbiformis SWALLOW. 

 Strophodonta cymbiformis Swallow, 1860: Trans. St. Louis Acsd. Sci., 



vol. I, p. 635. 

 Strophodonta sub cymbiformis Swallow, 1860: Trans. St. Louis Acad. Sci., 



vol. I, p. 635. 

 Strophodonta, kemperi Swallow, 1860: Trans. St. Louis Acad. Sci., vol. I, 



p. 636. 

 Strophcdovta inflexa Swallow, 1860: Trans. St. Louis Acad. Sci., vol. I, 



p. 637. 

 Strophodonta. boonensis Swallow, 1860: Trans. St. Louis Acad. Sci., vol. 



I, p. 638. 



Shell rather large, like S. demissa but with a broad, median 

 sinus and fold. 



Horizon and localities. Devonian, Callaway limestone : 

 Dauphin ( Callaway county ). 



