84 THE DEVONIAN OF MISSOURI. 



Hall's dtscription — "Shell semicircular or semielliptical, frequently unsymmetrical, 

 the proportions of length and breadth varying in different individuals; hingeline straight, 

 nearly or quite equal to or greater than the greatest width of the shell; sides nearly 

 rectangular to the hingeline, or curving inwards. Ventral valve more or less convex 

 towards the umbo and sometimes in the middle, curving downwards or flattened towards 

 the front and sides of the shell; beak often distorted; area vertical or inclined forwards 

 or backwards, usually unequal on the two sides of the foramen, which is closed by a 

 strong convex deltidial plate. Dorsal valve depressed convex, sometimes nearly flat 

 and sometimes very convex, with a narrow linear area; socket-plates strong, and sup- 

 porting the cardinal process, which is double and has sometimes a faint ridge between 

 the two divisions, which are themselves very short. Surface marked by sharp close 

 radiating crenulated striae, which increase mainly by interstitial additions." 



Remarks — The interiors are not preserved in any of the specimens from Missouri. 

 The outstanding features of the sbells are the crenulated striae which increase by 

 interstitial additions, the shape of the valves, and the strong convex deltidium. It 

 differs from Schuchertella parva from the Iowa Devonian in having a low area with the 

 shell not distorted. Specimens of a Schuchertella from the Lime Creek shale of Iowa 

 agree in every respect with the Missouri specimens but not with Hall's description of 

 5. parva. It is possible that a large series of specimens from the Lime Creek would show 

 that S. parva (Hall) is a synonym of 5. arctostriata (Hall). Hall used only one specimen 

 for illustration and description. 



Occurrence — Snyder Creek shale of Callaway County. 



Schuchertella cf. pandora (Billings) 



Plate 11, figures 5 and 14. 



1860. Streptorhynchus pandora Billings, Canadian Jour., V, p. 226, figs. 12, 13. 



1863. Streptorhynchus Pandora Billings, Geol. Canada, p. 369, fig. 384. 



1867. Streptorhynchus pandora Hall, Pal. New York, IV, pp. 68-70, pi. 4, figs. 11-19; 



pi. 9, figs. 18-25, 27. 

 1874. Streptorhynchus pandora Nicholson, Pal. Prov. Ontario, p. 70. 

 1883. Streptorhynchus chemungensis var. pandora Hall, Second Ann. Rep. N. Y. State 



Geol., pi. 40, figs. 1-6. 

 1892. Orthothetes chemungensis var. pandora Hall and Clark, Pal. New York, VIII, 



pt. 1, p. 255, pi. 9, fig. 30; pi. 10, figs. 1-6. 

 1897. Orthothetes pandora Schuchert, U. S. Geol. Surv., Bull. 87, p. 298. 

 1909. Schuchertella pandora Grabau and Shimer, North American Index Fossils, I, 



p. 229, fig. 279. 

 1912. Schuchertella pandora Kindle, Bull. U. S. Geol. Surv., 508, p. 76, pi. 3, figs. 



7 and 8. 

 Hall's description — "This shell, in its symmetrical form is somewhat semioval, 

 the length and width being about as four to five. A well-formed specimen, of one inch 

 in length, measures one and a quarter inches in width; hingeline equal to the greatest 

 width of the shell, and forming right angles with the sides, which are usually nearly 

 straight; the front broadly rounded; cardinal extremities sometimes a little salient, and 

 sometimes rounded. Ventral valve convex on the umbo, the greatest convexity being 

 at the apex, from which the surface slopes in a regular plane to the sides and middle of 

 the shell, becoming slightly concave below the middle of the shell, becoming slightly con- 

 cave below the middle and along the front; area large triangular, extending the entire 

 length of the hingeline, and inclining over the dorsal valve at an angle of about 110°. 

 The foramen has been large, about twice as wide at the base as the height, and is closed 

 by a convex deltidium. Dorsal valve moderately convex, a little flattened towards the 

 cardinal extremities, and curving towards the sides and front ; area narrow and linear. 



