594 GEOLOGY OF OHIO. 



occupy the fold, flanked on each side of the fold by one that is less dis- 

 tinct. The sinus contains one plication and its boundaries are formed by 

 two plications less distinct, especially along their exterior margin. All of 

 these broad plications as well as the sinus and fold soon disappear pos- 

 teriorly. The surface is marked by fine concentric striae of growth, visi- 

 ble under a lense. The general outline of the shell is circular. Among 

 published species it most closely resembles Camerella Ops, Billings, from 

 which however its general form will readily distinguish it, and Cyclospii a 

 biculcata, Emmons, a small Trenton form. No specimens showing the 

 hinge area or internal structure were found, and hence the generic de- 

 termination is largely a guess. 



Eichwaldia retictclata, Hall. 



(Plates 25, Figs. 4, a, b.) 



This species was found by Mr. E. M. Thresher at Fauver's Quarry, 

 and is represented by a specimen in his cabinet. 



Stricklandinia triplesiana, Foerste. 



(Plate 26, Figs 13, a, b, 14 



The hinge line almost equals the shell in width, and is not much shorter 

 than the length of the shell. Both valves slope posteriorly to the hinge 

 line, very much like the sides of a dull, cold chisel. Their convexity is 

 moderate and about equal in the two valves. A low median fold marks 

 the brachial valve, and a corresponding sinus the pedicle valve. Both 

 sinus and fold are indistinct at the beak, and become distinct features 

 first at five to ten millimeters from the beak, after which they broaden out 

 and become more accentuated anteriorly. Fine concentric striae of growth 

 are visible under a lense. The radiate fibrous structure of the shell is 

 also visible, perhaps owing to partial exfoliation. The type specimens 

 were found at the Soldiers' Home Quarry in the middle limestones. Since 

 then it has also been found at Huffman's Quarry. 



