210 
Kirtley F. Mather 
fidence to Hind’s species. The internal cast shows the typical 
subquadrate outline of the shells figured by Hind though it is 
much smaller than most of his figures, agreeing closely in size 
with figure 8. The groove which represents the thickened ridge 
of the hinge plate is well shown and the surface markings of 
concentric grooves and ridges are present. The external mold 
has preserved the surface ornamentations to the last detail and 
these agree with the description of the types except that the 
angular ridges are from 16 to 18 in number. Hind notes, how- 
ever, that there is “a great amount of variation in the size, 
number, and proximity of the concentric ribs.” 
The dimensions of the Kessler form are approximately : 
length, 11.5 mm. ; height, 8.6 mm. ; convexity, 4.1 mm. 
Horizon and locality. Kessler limestone : East Mountain, Fay- 
etteville, Arkansas (Station 209). 
NUCULID^ 
Genus NUCULA Lamarck 
Nucula parva McChesney 
Plate XV, figure 21. 
1860. Nucula parva. McChesney, Desc. New Pal. Foss., p. 54. 
Coal Measures: Danville, Illinois. 
1865. Nucula parva. McChesney, 111. New Spec. Foss., pi. 2, figs. 8a-c. 
1868. Nucula parva. McChesney, Trans. Chicago Acad. Sci., vol. 1, p. 
39, pi. 2, figs. 8a-c. 
1873. Nucula parva. Meek and Worthen, Geol. Surv. 111., vol. 5, p. 589, 
pi. 26, fig. 8. 
Coal Measures: Danville, Illinois. 
1888. Nucula parva. Keyes, Proc. Acad. Nat. Sci., Phil., p. 233. 
Lower Coal Measures: Des Moines, Iowa. 
1894. Nucula parva. Keyes, Mo. Geol. Surv., vol. 5, p. 121. 
Upper Coal Measures: Kansas City, Missouri. 
1897. Nucula parva. Smith, Proc. Am. Phil. Soc., vol. 35, p. 35. 
Lower Coal Measures: Conway County, Arkansas. 
Upper Coal Measures: Crawford County, Arkansas. 
1914. Nucula parva. Price, West Va. Geol. Surv., Preston County Rep., 
p. 514. 
Ames limestone: Throughout the County. 
Brush Creek limestone: Grant district; 0.9 mile west of and 0.9 
Mile northeast of Bruceton Mills, Garrett County,' Maryland, 4 
miles northwest of Oakland, and B. & O. R. R. cut at Hutton. 
