190 POTTSVILLE FAUNA OF OHIO 



ordinarily smaller than adult members of this species and its lateral 

 plications are invariably simple, as inferred from figures and descrip- 

 tions. It is not synonymous with S. rockymontanus." 



An examination of Marcou's figures of S. rockymontanus shows that 

 his species is marked with numerous, rather fine plications, freely bi- 

 furcating on the sides as well as in the sinus and on the fold. On the 

 right si,de of the fold on the large figure of the dorsal valve, there are 

 four bifurcated plications, while on the large ventral valve one of the 

 plications is apparently three-forked and at least sixteen lateral plica- 

 tions seem to be present. The hinge line as stated in the description 

 is shorter than the greatest width of the shell. Compared with S. 

 opimus, the contour is very similar as in both the length and width 

 are nearly equal, but the plications are finer, more numerous and freely 

 bifurcating. It is of significance also that Hall cites his species as 

 occurring in Ohio, while that of Marcou was described from a distant 

 locality. 



Horizon and locality. Widely distributed throughout the middle 

 and upper Pottsville formation excluding the Boggs and Sand Block 

 ore members: Lowellville, a; Lower Mercer, aa; Lower Mercer ore, a; 

 Upper Mercer, aa; McArthur, aa; Black Flint, a. 



Genus Ambocoelia Hall 

 Ambocoelia planoconvexa (Shumard) 



1855 Ambocoelia planoconvexa. Shumard, Geol. Rep. Mo., p. 202. 



Upper Coal Measures: On Missouri River, near mouth of Platte River. 



Description. This common and widely distributed Pennsylvanian 

 species has been found only in the McArthur limestone from two locali- 

 ties. Although it is rare in the Pottsville formation of this State, a 

 number of well-preserved specimens have been obtained. The indi- 

 viduals are all small, one of average size measuring: length 5.5 mm. ; 

 width 5 mm., convexity 2.5 mm. 



Horizon and locality. McArthur limestone: Jackson County, Lo- 

 cality 80, r; Hocking County, Locality 86, r. 



Ambocoelia planoconvexa (Shumard) var. 



Description. A small brachiopod belonging to the genus Ambo- 

 coelia is common in the black shales on the Lowellville horizon along 

 Poverty Run, Muskingum County. The form suggests identification 

 with Ambocoelia planoconvexa (Shumard), but fairly constant differ- 



