110 THE DEVONIAN OF MISSOURI. 



A. fultonensis (Swallow) shows decided and constant differences from A. vittata 

 Hall. An average specimen of A. vittata Hall from the Cedar Valley of Iowa gives the 

 following measurements: Length, 11 mm.; breadth, 12 mm.; thickness, 7.5 mm. An 

 average A. fultonensis (Swallow) from Callaway County gives: Length, 7.5 mm.; 

 breadth, 6.5 mm.; thickness, 4.5 mm. 



The ratio of length to breadth of the Iowa form is 11:12, of the Missouri form 15-13. 

 The greater width compared to length is constant with the Iowa form while the reverse 

 is true of the Missouri form. The largest specimen examined by the writer is 9 mm. 

 wide by 8.8 mm. long, and measurements have been made of only two specimens that 

 are wider than long. Swallow must have selected unusually large specimens for his 

 description. Some of the largest specimens have fairly well defined fold and sinus which 

 are much narrower than in Iowa specimens of A. vittata Hall. The beak of the pedicle 

 valve is much narrower and projects farther behind the hinge line than in A. vittata Hall. 



Callaway limestone specimens of A . fultonensis may be distinguished from Snyder 

 Creek specimens on account of being thinner and broader, but this seems to be due to 

 flattening from pressure. The average size is larger in the Callaway. 



Occurrence — Abundant in the Snyder Creek shale of Callaway County, particular- 

 ly near New Bloomfield. Most of the Snyder Creek specimens are less than 8 mm. 

 in length. Rare in the Callaway limestone of Callaway, Montgomery and Boone 

 Counties. 



Athyris vittata (Hall) 



Plate 17, figures 8-10, 15, 16. 



1860. Athyris vittata Hall, Thirteenth Rep. New York State Cab. Nat. Hist., pp. 89-90. 



1897. Athyris fultonensis Schuchert, Bull. U. S. Geol. Surv., 87, p. 147. 



1901. Athyris fultonensis Kindle, Indiana Dept. Geol. Nat. Res., 25th Ann. Rept., 



pp. 597-598. 

 1909. Athyris fultonensis Grabau and Shimer, North American Index Fossils, I, pp. 



352-353, fig. 460. 

 1911. Athyris fultonensis Cleland, Wisconsin Geol. Nat. Hist. Surv., Bull. 21, pp. 



83-84, pi. 14, figs. 1-4. 

 1915. Athyris fultonensis Butts, Geol. Surv. Kentucky, ser. 4, III, pt. 2, pi. 45, figs. 



3,4. 

 Hall's description — "Shell ovate, subquadrate, gibbous with the mesial fold and 

 sinus distinct; front conspicuously sinuate; hinge line short; cardinal extremities rounded. 

 Ventral valve gibbous above, more convex than the dorsal; umbo prominent; the beak 

 incurved and truncated in the plane of the longitudinal axis by a round foramen, curv- 

 ing very abruptly to the cardinal and cardino-lateral margins; the center marked by a 

 well-defined mesial sinus, which is continued nearly or quite to the beak and becoming 

 much deeper and subangularly margined towards the front. Dorsal valve a little less 

 gibbous than the ventral, sides regularly curving; the middle of the upper part distinctly 

 prominent, and developed below in a strong mesial fold which is abruptly elevated in 

 front. Surface marked by regularly imbricating lamellose lines of growth, which 

 on the better preserved surfaces are finely crenulated on their edges and intermediate 

 spaces striate." 



Remarks — Specimens from the Mineola of Missouri show several variations from 

 the Iowa specimens though the differences are not important. The greatest convexity 

 of the pedicle valve is nearer the front margin in the Mineola specimens. The beak 

 of the pedicle valve does not project as far back of the hinge line in the Missouri speci- 

 mens as in the Io\va specimens. In most cases the fold and sinus are somewhat broader 

 in the Iowa specimens than in the Missouri. The Missouri specimens are thicker com- 

 pared to length than the Iowa specimens. 



Occurrence — Mineola of Ralls and Montgomery Counties. Abundant in Ralls 

 County. 



