652 GEOLOGY OF OHIO. 



Muscular scar situated lower than usual, placed just behind the center of 

 the valves. Surface of cast with distant lines of growth in the outer 

 half. 



The hinge is shorter and the anterior excavation larger than in C. 

 lamellosa and C. erecta, two species of the lower Trenton rocks of Min- 

 nesota and Wisconsin. 



Formation and locality: Upper beds of the Cincinnati group, Rich- 

 mond, Indiana, where the specimen described was collected for the author 

 hy Mr. John Misener. 



Family MODIOLOPSID^, (Fischer) Ulrich. 



Genus Modiolodon, Ulrich. 



Cyrtodonta {part), Safford, 1869, Geology of Tennessee. 



Modiolodon, Ulrich, 1893, Final Rep., Vol. Ill, Geol. and Nat. Hist. Sur. Minn.. 

 521. 



Modiolodon oviformis, Ulrich. 



Plate 53, Figs. 7 and S. 



Modiolopis Oviformis, Ulrich, 1890, American Geologist, Vol. V, p. 276. 



Shell 50 mm. or less in length, slightly oblique, almost regularly 

 oval transversely, narrowest in the anterior half; greatest height and 

 length as three or three and one half is to five. Valves moderately and 

 nearly uniformly convex, the point of greatest convexity a little in front 

 and above the center. Cardinal margin arcuate, basal margin with 

 nearly the same amount of convexity; anterior and posterior ends nicely 

 rounded, the latter much the widest and often produced slightly bej^ond 

 an even curve in the lower part. Beaks small, inconspicuous, and situ- 

 ated a very short distance behind the anterior extremity in the shell, ap- 

 pearing more prominent and less nearly terminal in casts of the interior; 

 umbonal ridge nearly obsolete. Shell of moderate thickness, strongest 

 in the umbonal region, its outer surface nearly smooth, exhibiting only a 

 few faintly impressed fine concentric lines. Hinge with two subequal, 

 nearly horizontal rather strong cardinal teeth, in each valve, situated 

 mostly in front of the beaks and above the strongly impressed anterior 

 muscular scars. 



Casts of the interior, in which condition the species is usually found, 

 are in most cases terminated anteriorly by the well marked pair of mus- 

 cular scars. Pallial line simple, distinct and pustulose in the anterior 

 third, behind which it is obscurely defined to the large and faintly im- 

 pressed posterior adductor scar. The latter is obovate and situated close 



