size from the Lower Mercer limestone measures: length 16 mm., 

 width 19.5 mm., convexity 5 mm. 



Horizon and locality. Boggs limestone: Symmes Creek, Mus- 

 kingum County (Locality 29), r. Abundant and generally distributed 

 throughout the Lower Mercer limestone and the higher Pottsville 

 horizons. 



Genus Hustedia Hall and Clarke 

 Hustedia mormoni (Marcou) 



1858 Terebratula mormoni. Marcou, Geol. North Ame ica, p. 51, PI. 6, Fig. 11. 



Mountain L.S.: Salt Lake City, Utah. 

 1894 Hustedia mormoni. Hall and Clarke, Int. to Study of Brach., Pt. 2, PI. 37, 



Figs. 13-20. 



Coal Measures: Near Kansas City, Missouri. 



Although this little species is abundant and wide-spread in rocks 

 of Pennsylvanian age, it is particularly characteristic of the upper part 

 of the system, so that its appearance in the basal member of the Potts- 

 ville formation in Ohio is of interest, especially as it has not been 

 found in any of the higher members of that formation. The form is 

 common in the Harrison ore, and with the exception of a few cases 

 where the entire shell has been replaced by calcite, it occurs only as 

 internal and external molds. Occasionally the spiralia and crura 

 are preserved. 



Dimensions. A specimen of average size measures: length 

 7 mm., width 4.5 mm., convexity 4 mm. 



Horizon and locality. Harrison ore: Jackson County (Locality 

 D,c. 



Genus Composita Brown 

 Composita subtilita (Hall) 



1838 Terebratula argentea. Shepard, Am. Jour. Sci., 1st Ser., Vol. 34, p. 152, Fig. 8. 



Limestone: Western Bluff of Little Vermilion River, Illinois. 

 1852 Terebratula subtilita. Hall, Stansbury's Exped. Great Salt Lake of Utah, 



p. 409, PI. 2, Figs. 1, 2. 



Carboniferous: Missouri River, near Weston. 



This form constitutes without doubt the most widespread and one 

 of the most abundant fossils of the Pottsville formation of Ohio. It 

 is common in the Harrison and Sharon ores at the base, and is found 

 in almost every other fossiliferous horizon to the Black Flint member 

 at the top. It occurs in great profusion in the Lower Mercer and 

 McArthur limestones. The specimens from the Harrison ore often 

 have the spiralia and even the jugum preserved in an unusual manner. 

 The measurements of a large specimen from the Harrison ore are: 

 length 18 mm., width 16 mm., convexity of ventral valve 5 mm.; 

 from the Lower Mercer limestone: length 24 mm., width 22 mm.., 

 convexity 12 mm, 



Horizon and locality. Harrison ore: Jackson County (Locality 1), 

 c. Sharon ore: Lick Run, Scioto County (Locality 2), c. Abundant 



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