70 PALAEONTOLOGY OF OHIO. 



Genus TREMATIS, Sharpe. 

 Trematis millepuxctata. 



Plate 1, figs. 4-7. 



Trematis millepunctata, Plall; Ext. 20th Rept. State Cab., p. 14, 1866. 

 Trematis millepunctata, Hall; 24th Rept. State Cab., p. 221, pi. 7, figs. 22-25. 



Shell small or medium sized, sub-orbicular, slightly transverse on the 

 ventral side and lenticular in profile. Ventral valve strongly convex 

 below the middle, more dej^ressed above, and with a narrow, deeply de- 

 pressed pedicle- opening extending to the cardinal border, the margins 

 being flattened for a space nearly equal to the breadth of the opening. 

 Dorsal valve more elongated than the opposite, most convex above the 

 middle ; beak pointed, and projecting considerably beyond the cardinal 

 margin of the ventral valve, and having a depressed or concave triangu- 

 lar area. 



Interior of the dorsal valve marked near the middle by two compara- 

 tively large, semi-circular or reniform muscular scars; the breadth across 

 the two more than equals one-third the diameter of the valve, and in the 

 center of the valve by a slight mesial septum. 



Surface strongly punctate in concentric curves passing from the center 

 of the shell outwards, extending through the substance of the shell near 

 the front margins of the valves, and distinctly marking the internal 

 casts left by the decomposition of the shell ; inner layers of the shell not 

 punctate. 



This species has been commonly identified with T. terminalis=Orbicula 

 lerminalis, Emmons. It differs, however, from that species in the more 

 transverse form, less convexity of the ventral valve, and prominent 

 beak of the dorsal ; as also in not having the puncta passing entirely 

 through the substance of the shell as they do in that species. 



Formation and locality: In the shales of the Hudson River group, at Cincinnati, 

 Ohio. 



Trematis puncto striata. 



Plate 1, figs. 8, 9. 

 Trematis punctostriata ; 23d Rept. State Cab., p. 243, pi. 13, figs 17, 18. 



The following is the description of this species as given in the 33d 

 Report : 



"Shell of medium size, oblate, with the rostral border somewhat pro- 

 truding, giving a broadly oval form to the upper valve. Upper valve 



