183 Systematic Paleoxtology — Middle Devonian 



in part of the specimens with a median depression below the middle of 

 the valve. There is a narrow cardinal area interrupted in the middle by a 

 wide, convex chilidiiim. Tn the interior of this valve a median septum 

 extends from the anterior part of the cardinal process to the anterior 

 third of the shell. Surface marked by about eighteen to twenty broad, 

 simple, rounded plications which are generally wider than the interspaces. 

 There are fine, undulating, concentric striae, and a few stronger imbri- 

 cating lamellae mark the stages of growth of the shell. 



The specimens from Maryland show about all the forms of this species 

 which are represented in the Palseontology of New York (see vol. iv, pi. 

 Ixii), as from the arenaceous,ferruginous shales east of Hancock are speci- 

 mens similar to figures oc and 3e, while the bluish, slightly calcareous 

 shales at 21st Bridge contain very large forms, even larger than figure 31 

 of the N. Y. Palaaontology, which are likewise characterized by coarse 

 plications that become inconspicuous on the thickened margin of the shell. 

 The figiires of the Maryland specimens show one of nonnal size and 

 another of the large form. Not infrequently the shell substance is well 

 preserved and the punctate structure beautifully shown. 



Length of average adult, 20 mm.; width, 25 mm.; length of large speci- 

 men, 28 mm. ; width, 38 mm. 



Occurrence. — Eomney Formation, Hamilton Member. B. & 0. E. E. 

 cu.t at 21st Bridge. Williams Eoad, 3I/2 miles southeast of Cumberland; 

 east bank Evitts Creek below Wolfe Mill; Williams Eoad, % mile east 

 of Queen City Hotel, Cumberland; Williams Eoad, 14 mile east of 

 Queen City Hotel, Cumberland ; Town Creek Eoad at George Diefen- 

 baugh's; B. & 0. E. E. cut at 21st Bridge; on National Eoad, i/^ mile 

 west of Tonoloway Eidge; on Oldtown Eoad east of Maryland Ave., 

 Cumberland; McCoys Ferry; southwest of McCoys Feriy; on the Han- 

 cock-Harrisonville Eoad about 2 miles north of Hancock; in run at 

 Hancock east of Catholic church; along Plintstone Creek in Gilpin; 

 on National Eoad in Gilpin ; west of iron bridge over Town Creek north- 

 east of Oldtown; on National Eoad i/^ mile west of Licldng Creek; on 

 road east of Pine Hill about 4 miles north of Oldtown; B. & 0. E. E. cut at 

 Hancock Station. W. Va. ; on road about half way between Eomney and 



