136 THE DEVONIAN OF MISSOURI. 



1892. Stropheodonta {Leptostrophia) perplana Hall and Clarke, Pal. New York, VIII, 



pt. I, p. 288, pi. 15, figs. 2-13. 

 1897. Stropheodonta perplana Schuchert, Bull. U. S. Geol. Surv. 87, pp. 425-426. 

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



pp. 618-619, pi. 5, figs. 3-7. 

 1909. Stropheodonta (Leptostrophia) perplana Grabau and Shimer, North American 



Index Fossils, I, pp. 217-218, fig. 264. 

 1911. Stropheodonta perplana Cleland, Wisconsin Geol. Nat. Hist. Surv., Bull. 21, 

 p. 89, pi. 18, figs. 1-4. 



Hall's description — "Shell semi-elliptical; the length varying from two-thirds to 

 three-fourths the width, which is from half an inch to two inches; slightly concavo- 

 convex, and often nearly flat; hinge line equalling or often a little greater than the 

 width of the shell below; the extremities usually somewhat salient, except in extremely 

 old shells. Margins of the shell often a little contracted just below the hinge-extremities, 

 making the width less than below; but the sides are frequently nearly straight for half 

 their length, and the front broadly rounded with the margin attenuate. 



Ventral valve very little convex, the greatest convexity above the middle of its 

 length, with frequently a few obscure concentric wrinkles near the apex, and sometimes 

 upon the body of the shell; apex scarcely rising above the hinge line, and slightly in- 

 curved. Dorsal valve gently concave, and often nearly flat. 



Area of the ventral valve usually less than a line in width, inclined at an angle 

 of 40 to 50 to the plane of the margins and curved in the upper part, vertically striated 

 in its whole extent and crenulate on the inner margin; sometimes a flat triangular space 

 in the place of a foramen, with a narrow callosity in the middle, but this feature is not 

 always observable. Area of the dorsal valve about half as wide as that of the ventral, 

 gently curved outwards, leaving an angle between the two or more than 90; the centre 

 is marked by a narrow callosity or an impressed space. 



Surface covered by fine subequal striae, those of the ventral valves being the 

 finer, extremely sharp and often gently undulating, increasing both by bifurcation and 

 intercalation, and crossed by fine, even concentric striae. In some specimens the longi- 

 tudinal striae rise at frequent and regular intervals into minute granules, evidently 

 the bases of minute spines, which have covered the surface of the ventral valve. The 

 dorsal valve is marked by fine even rounded striae which are cancellated by close con- 

 centric striae, and the same obscure concentric undulations as are observed on the sur- 

 face of the ventral valve. Very rarely there is some interruption to the regularity of the 

 striae, apparently owing to an injury which has often caused the concentric striae to 

 curve towards that point, and the radiating striae to converge making a kind of seam 

 of cicatrix." 



Remarks — The remains of this species from southeastern Missouri are all from a 

 sandstone member of the St. Laurent. None of them is well preserved. The fineness of 

 plications, flatness of valves, and shape of muscular area form the main basis for identi- 

 fication. 



Genus Pholidostrophia Hall and Clarke 



Pholidostrophia iowaensis (Owen) 

 Description and synonomy on pages 82 and 83 



A specimen from the Mineola is figured on plate 11 at figure 9. 



Remarks — Five specimens from the Grand Tower limestone of Little Saline Creek, 

 Ste. Genevieve County, are in the collections of the Walker Museum. All of the speci- 

 mens are imperfect. The species is rare in the fauna. 



