278 Systematic Paleoxtology — Middle Devoxiax 



prominent characters are their medium size; nearly circular outline; and 

 strong, irregular concentric ridges. 



Length, medium size, 12, 13 mm. ; height, 12 mm. 



There is a large specimen from l\'[cCoys Ferry which is somewhat elon- 

 gated by pressure and measures 29 mm. in length by 27 in height (plate 

 xxxiv, fig. 15). This has very strong concentric ridges which usually 

 divide at a distance from the margins. It has not been separated from P. 

 liraia, because but a single specimen is known although it may prove to 

 be distinct enough to form a new variety. The specimen was submitted 

 to Dr. Grabau who wrote " I think perhaps the stronger compound 

 wrinkles would make this a distinct variety of P. lirata." 



Occurrence. — Eojiney Formation, Hamilton Member. East bank 

 Evitts Creek below Wolfe Mill ( ?) ; McCoys Ferry; southwest of McCoys 

 Ferry; on Oldtown Eoad east of Maryland Ave., Cumberland; on Han- 

 cock-Harrisonville Eoad about 2 miles north of Hancock; on National 

 Eoad in Gilpin; west of Lock Xo. ^G at Great Cacapon; W. Va. side 

 Potomac Eiver about 3 miles south of Cumberland. 



Collections. — Maryland Geological Survey ; Xew York State Museum ; 

 American Museum of jSTatural History. 



Paracyclas tenuis Hall 

 Plate XXXIV, Figs. 16, 17 



Paracyclas tenuis Hall, 1883, Pal. N. Y., vol. v, pt. i, plates and explanations, 



pi. Ixxii, figs. 20-22. 

 Paracyclas tenuis Hall, 1885, Pal. N. Y., vol. v, pt. i, Lamelllbranchiata ii, 



p. 443, pi. Ixxii, figs. 20-22; pi. xcv, fig. 25. 

 Paracyclas tennis Clarke, 1903, N. Y. State Mus., Bull. fi5, p. 485. 



Description. — "Shell small, subcircular; length and height about 

 equal; margins regailarly curving; cardinal line short. Valves moderately 

 convex; beaks a little anterior to the middle, small, closely appressed, 

 scarcely rising above the hinge-line; post-cardinal slope curved and rap- 

 idly declining backward, limited by the ligamental groove, which is very 

 distincth marked. Test extremely thin; surface marked by very fine 

 concentric striae, which are sometimes aggregated into fascicles toward 

 the pallial margin." Hall, 1885. 



