202 Systematic Paleontology — ^Middle Devoxiax 



the surface of this species is marked by " very fine radiating and concentric 

 striae." In most of the specimens, both in my collection and in other collec- 

 tions bearing the name A. umbonata, the surface is smooth. In some specimens, 

 however, concentric striae are well developed but none have been observed 

 showing radiating striae. Shells with a strongly lamellose dorsal valve are 

 not uncommon. These as well as smooth shells frequently show a distinct fold 

 near the front of the dorsal valve. 



Length, 6-10 mm.; width, 8-12 mm. There are some specimens 

 smaller than the normal ones, hut apparently belonging to this species, 

 which have a length and width of about 4 mm. 



Occurrence. — Eomney Formation, Onondaga Member. Williams 

 Road, 3I/2 miles southeast of Cumberland; Hancock; Hanging Eock, 

 W. Ya. Hamilton Member. Williams Eoad, 31/^ miles southeast of 

 Cumberland ; east bank E\itts Creek below Wolfe Mill ; Williams Eoad, 

 1/4 mile east of Queen City Hotel, Cumberland ; in Jennings Eun, V2 

 mile west of Corriganville; Town Creek Eoad at George Diefenbaugh's ; 

 Licking Creek east of Warren Point; on Oldtown Eoad east of Mary- 

 land Ave., Cumberland; Ernstville; in run at Hancock east of Catholic 

 church ; along Flintstone Creek in Gilpin ; on Xational Eoad m Gilpin ; 

 west of iron bridge over Town Creek northeast of Oldtown ; on Eomney- 

 Hanging Eock Eoad, about |- mile north of Eomney, W. Va. ; 1 mile 

 north of Eomney, W. Ya. ; B. & 0. E. E. cttt at Hancock Station, W. Ya. ; 

 W. Va. side Potomac Ei\er, 4 miles south of Cumberland. 



Collections. — ^laryland Gieological Survey; American ]\[useum of 

 Xatural History. 



Ambocoelia virgtniana n. sp. 



Plate XX, Figs. ;i-G 



cf. Ambocoelia umbonata var. cf. nana Kindle, 1912, Bull. U. S. Geol. Surv., 

 No. 508, p. 83, pi. V, figs. 20-23. 



Description. — Shell very small; plano-convex; hinge-lino straight, less 

 than the greatest width of the shell, cardinal angles rounded. Yentral 

 valve gibbous, umbo elevated with incurved beak ; a narrow deep mesial 

 sinus which is sharply defined extending from the beak to the front of the 

 shell; part of the specimens show a single plication beginning near tlie 

 center of the valve, extending to its front and bordering the sinus. Dor- 



