210 POTTS VILLE FAUNA OF OHIO 



Description. This species of Parallelodon appears in the Lowell- 

 ville limestone but is most characteristic and abundant in the Lower 

 Mercer. It is distinguished from the other species of Parallelodon 

 occurring in this State by the apparent absence of all surface 

 markings. The obscure, fine, radiating lines of the posterior-dorsal 

 region, referred to by Meek 1 do not* appear on the specimens examined. 

 The individuals from the Lowellville limestone are all imperfectly pre- 

 served, so that their identification is not accompanied by a great degree 

 of certainty. A specimen of average size from the Lower Mercer lime- 

 stone measures: length 27.5 mm., maximum height 11.5 mm., convexity 

 of right valve 5.5 mm. 



Horizon and locality. Lowellville limestone: Muskingum County, 

 Locality 19, r. Widely distributed in the Lower Mercer member, c. 

 Me Arthur member: Jackson Co'unty, Locality 80, r; Vinton County, 

 Locality 85, c. 



Parallelodon sangamonensis (Worthen) 

 PL XI, figs. 3, 4 



1890 Macrodon sangamonensis. Worthen, Geol. Surv. 111., Vol. 8, p. 123, PI. 21, 

 Figs. 3, 3a. 

 Coal Measures: Sangamon County, Illinois. 



Description. This form is rare in the Pottsville formation of 

 Ohio, and where present is only about one-half the 'size of the Illinois 

 specimens; an individual of average size measures: length 24 mm., 

 height from beak to ventral margin 13 mm. Extending from the beak 

 to the posterior margin there are generally six strong, rounded ribs; 

 the remainder of the shell is smooth or marked by fine, radiating lines. 

 The general contour resembles Worthen's species so closely the identi- 

 fication is made with considerable confidence. 



Horizon and locality. Lowellville limestone: Mahoning County, 

 Locality 22, r. Widely distributed in the Lower Mercer limestone of 

 Perry, Muskingum, and Licking counties, r. Lower Mercer ore: 

 Jackson County, Locality 56, r. Upper Mercer member: Muskingum 

 County, Locality 68, r. McArthur member: Jackson County, Locality 

 80, r; Vinton County, Locality 84, r. 



Parallelodon tenuistriatus (Meek and Worthen) 

 PL X, figs. 30, 31 



1866 Area striata. Geinitz, Die Garb, und Dyas in Nebraska, p. 20, Tab. 1, Fig. 32. 



(Non Mytilites striatus Schloth., 1817.) 

 Nebraska City, Nebraska. 



1867 Macrodon tenuistriata. Meek and Worthen, Proc. Chicago Acad. Sci., Vol. 1, 



p. 17. 



Upper Coal Measures: Springfield, Illinois. 



x Meek, F. B., Pal. Ohio, Vol. II, p. 334, 1875. 



