74 THE DEVONIAN OF MISSOURI. 



exceptional in Missouri specimens as it is in Iowa specimens; normal individuals are 

 no more gibbous than normal individuals from New York or Maryland. The de- 

 pression on the ventral valve is broader and shallower than in average specimens from 

 Iowa though many Iowa specimens are similar to those from Missouri; the average 

 Missouri specimens are normal for 5. striatula. The emargination of average Missouri 

 specimens is about the same as for average 5. striatula and not as deep as in the Iowa 

 specimens. 



The Snyder Creek specimens are typical 5. striatula though one extreme is like the 

 typical 5. iowensis Hall and Clarke. 



Occurrence — Abundant in the Snyder Creek shale of Callaway and Montgomery 

 Counties; rarely found in the Callaway limestone of the same counties. 



Schizophoria cf. propinqua (Hall) 



Plate 11, figure 4 



1857. Orthis propinqua Hall, Tenth Rep. N. Y. State Cab. Nat. Hist., p. 110. 

 1867. Orthis propinqua Hall, Pal. New York, IV, pt. 1, p. 43, pi. 5, fig. 3. 

 1883. Orthis propinqua Hall, Second Ann. Rep. N. Y. State Geol., pi. 36, figs 30 and 31. 

 1892. Schizophoria propinqua Hall and Clarke, Pal. New York, VIII, pt. 1, pp. 212, 



226, pi. 6, fig. 30. 

 1897. Schizophoria propinqua Schuchert, U. S. G. S. Bull. 87, p. ^74. 

 1909. Schizophoria propinqua Grabau and Shimer, North American Index Fossils, I, 

 p. 268. 



Hall's description — "Shell somewhat transversely elliptical or subquadrate, the 

 front truncate or emarginate, and the sides little curved, varying from moderately to 

 extremely gibbous; hinge-line equaling or a little greater than half the width of the shell. 

 Dorsal valve the larger and much the more gibbous; the greatest convexity a little above 

 the middle of the length curving abruptly to the sides and beak, and a little more 

 gently to the front; sometimes a little concave just within the cardinal angles; area 

 inclined to the area of the opposite valve, and about one-half or two-thirds as wide; 

 dorsal beak full, broad and rounded or obtusely pointed, extending a little beyond and 

 slightly incurved over the area. Ventral valve less gibbous than the dorsal, very promi- 

 nent on the umbo, sloping very abruptly to the cardinal angles and more gently towards 

 the lateral and basolateral margins, flattened in the centre; the lower half marked by a 

 gradually increasing, broad and undefined sinus, which gives a strongly curved outline 

 to the front margin; beak more acutely pointed and incurved ;- area elevated and in- 

 curved, its length equalling or greater than half the width of the shell. The beaks 

 of the two valves are approximate. 



Surface marked by fine unequal striae which increase by interstitial additions, and 

 are crossed by fine concentric striae, and, at unequal intervals, by stronger imbricating 

 lamellose lines of growth. In certain conditions of the surface, the striae show tubular 

 openings at the concentric lamellose lines. There are from eight to ten of the larger 

 striae in the space of two lines; and by counting the finer intermediate striae, there are 

 sometimes from thirteen to eighteen in the same space. The cast of the dorsal valve 

 shows a subquadrate or quadrate-ovate muscular scar, with a deeply marked border 

 and longitudinal median groove; a groove passes from the centre of the median line 

 obliquely to the lower lateral angles, dividing the adductor muscular scar. The vascular 

 impressions radiate from the muscular impression in broad bands, dividing several times 

 before reaching the margin of the shell." 



Remarks — Only two specimens are in our collections and as only the exteriors are 

 exposed the identification is uncertain. One of the specimens has a more pronounced 

 sinus than any specimens examined from Iowa and Michigan. 



Occurrence — Mineola of Montgomery and Warren Counties. 



