134 THE DEVONIAN OF MISSOURI. 



Order Protremata 



Superfamily Orthacea 

 Family Rhipidomellidae 

 Genus Schizophoria King 



Schizophoria striatula (Schlotheim) 



For synonomy and description see p. 72. Specimens of this 

 species are figured on plate 15. 



Specimens of 5. striatula (Schlotheim) from the Grand Tower are not as well 

 preserved as those from the Snyder Creek shale but they are like the Snyder Creek 

 specimens in every respect. Specimens are abundant on Little Saline Creek, Ste. 

 Genevieve County. The species occurs, rarely, in the Beauvais sandstone. 



Superfamily Strophomenacea 

 Family Strophomenidae 

 Genus Stropheodonta Hall 



Stropheodonta concava Hall 

 Plate 32, figure 12 



1857. Strophomena (Stropheodonta) concava Hall, Tenth Rep. N. Y. State Cab. Nat. 



Hist., pp. 115, 140, fig. 1. 

 1867. Stropheodonta concava Hall, Pal. New York, IV, pp. 96-98, pi. 16, figs, la-lh; 



pi. 14, figs. 2 a-d. 

 1897. Stropheodonta concava Schuchert, U. S. Geol. Survey, Bull. 87, p. 420. 

 1901. Stropheodonta concava Kindle, Indiana Dept. Geol. Nat Res., 25th Ann. Rep., 



pp. 619-620, pi. 5, figs. 1, la, 2; pi. 6, fig. 1. 

 1909. Stropheodonta concava Grabau and Shinier, North American Index Fossils, I, 



p. 216, fig. 261. 

 1913. Stropheodonta concava Prosser and Kindle, Maryland Geol. Surv., Middle and 



Upper Devonian, pp. 139-140, pi. 10, figs. 6, 7. 

 Hall's description — "Shell large, from two to three and a half inches wide on the 

 hinge line, concavo-convex or subhemispheric, broadly semi-elliptical or subcircular, 

 sometimes subtriangular from becoming narrowed in front. The proportions vary from 

 nearly equal length and breadth to a width one-fourth to one-third greater. The hinge 

 extremities are sometimes salient, but often rounded. 



Ventral valve varying from moderately to extremely convex, and becoming gibbous 

 in the middle, rounded upon the umbo and little elevated above the hinge line, with 

 beak small and scarcely incurved; in some specimens, the centre of the valve is elevated 

 in a median ridge. Dorsal valve usually almost flat or slightly concave in the upper 

 and central portions, becoming suddenly deflected towards the margin; in some speci- 

 mens, regularly concave. 



Area of the ventral valve nearly on a plane with the axis of the shell, about a line in 

 width, gently narrowing towards the extremities, vertically striated, with the margin 

 crenulated for moie than half the distance from the centre to the extremities. Area of 

 the dorsal valve almost rectangular in that of the ventral valve, very narrow and nearly 

 linear throughout. Sometimes narrower in the middle, tstriate and crenulate as in the 

 opposite valve; with a small, smooth triangular space beneath the apex. 



The surface of the ventral valve is marked by sharply elevated, strongly crenulated 

 striae, between which are sometimes one or two less elevated striae similarly crenulated, 



