340 Bepoet of the State GEOLoaiST. 



slightly convex in the umbonal region, but is depressed outward 

 in all directions, most strongly in the median line. The brachial 

 valve is depressed about the beak, convex over the pallial region 

 and divided in the median line by a shallow sinus. The interior 

 characters of the valves are essentially the same as those in 

 Orthis subquadrata. 



External surface covered with numerous fine, elevated strise, 

 alternating in size and crossed by finer concentric lines. 



Length of an average specimen, 18 mm.; width, 21 mm. 



Trenton horizon. Fountain, Minnesota. 



Orthis? Saffordi. 



Plate 4, figs. 10-12. 



Orthis 9 Saffordi, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 340, pi. 

 V a, figs. 38-40. 1892. 



Shell semielliptical in outline ; valves sub equally convex, the 

 pedicle-valve being the more elevated at the apex. Hinge-line 

 long and straight, giving the shell a strophomenoid appearance. 

 Cardinal area low ; delthyrium uncovered. 



Surface covered with numerous rounded, sharply elevated 

 striae, increasing by intercalcation, and crossed by exceedingly 

 fine concentric lines. The details of the interior are not known, 

 but the relations of the shell to Orthis are demonstrated by the 

 open delthyrium and simple cardinal process, slightly lobate on 

 its pcsterior face. 



Length of the type specimen, 17 mm.; width along the hinge, 

 22 mm. 



Trenton horizon. East Tennessee. 



Orthis (Dalmanella) arcuaria. 



Plate 4, figs. 13, 14. 

 Orthis {Dalmanella) arcuaria, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, 

 p. 341, pi. V c, figs. 20, 21. 1892. 



Shell with a general similarity to that of Orthis elegantula, 

 Dalman, but having the marginal outline more circular, the 

 pedicle-valve more evenly convex, the umbo more prolate, and 

 the brachial valve considerably more convex. The pedicle-valve 

 bears a broad fold, and the brachial a shallow sinus, in the median 

 line. In the interior of the pedicle-valve the muscular area is 



