and can be distinguished by its large size and by the numerous, regular, 

 concentric ridges covered with small spines which mark the surface. 

 An almost perfect specimen from the Boggs limestone measures: 

 length 40 mm., length of hinge line 30 mm., width 38 mm., convexity 

 22 mm. 



Horizon and locality. Boggs limestone: Blunt Run, Muskingum 

 County (Locality 27), r; Rock Cut, Muskingum County (Locality28),r. 



Genus Marginifera Waagen 



Marginifera muricata var. missouriensis Girty 

 PI. IV, Figs. 1, 2, 3. 



1915 Marginifera muricata var. missouriensis. Girty, Missouri Bureau Geol. and 

 Mines, Vol. XIII, 2nd Ser., p. 350, PI. XXX, Figs. 2-5a. 



Description. This little brachiopod is one of the most abundant 

 and widely distributed forms of the Ohio Pottsville formation, as 

 it is present in all the marine limestone horizons except the Boggs; 

 it occurs in extreme profusion at some localities in the Lower Mercer 

 member. The shells are small with the ventral valve gibbous, im- 

 parting a globular appearance to the form. The surface is marked 

 by rather fine, regular costae, crossed by concentric wrinkles which 

 on some specimens reach anteriorly two-thirds the length of the shell; 

 spines are numerous on all parts of the shell. The slight, ill-defined 

 fold near the anterior margin of the ventral valve, mentioned by Girty 

 on the Missouri forms, is absent on the specimens from Ohio; this 

 character, however, is not a constant one. 



Dimensions. The measurements of a ventral valve of average 

 size are: length 11 mm., width 13.5 mm., convexity 3.2 mm.; of a 

 dorsal valve: length 10.5 mm., width 12.5mm.; convexity 3.2 mm. 



Horizon and locality. Lowellville limestone: universally dis- 

 tributed. Abundant throughout the Lower Mercer and higher 

 horizons of the Pottsville formation. 



Marginifera wabashensis Norwood and Pratt en 



PL IV, Figs. 4, 5. 

 1854 Productus wabashensis. Norwood and Pratten, Jour. Acad. Nat. Sci. Phil., 



2nd Ser., Vol. 3, p. 13, PI. 1, Figs. 6a-d. 



Coal Measures: near New Harmony, Indiana. 

 1903 Marginifera wabashensis var. Girty, Prof. Paper, U. S. Geol. Surv., No. 16, 



p. 375, PL 5, Figs. 8, 8a. 



Carboniferous: Colorado. 



Description. This common and characteristic fossil is found 

 everywhere in the marine limestones of the Pottsville formation, 

 although it is especially abundant in the Lower Mercer and McArthur 

 limestones. It is generally found in an excellent state of preservation. 

 The ventral valve is very gibbous or even globular, having the greatest 

 curvature in the posterior third of the shell. The hinge line is ex- 

 tended forming the point of greatest width; the beak is small, depressed 



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