MARYLAND GEOLOGICAL SURVEY 367 



" Surface of the valves smooth, rising into an obtusely pointed promi- 

 nence at the anterior third of the length ; basal margins of the valves not 

 overlapping, so far as can be ascertained/' Hall and Whitfield, 1875. 



This minute o^tracod may be readily recognized .by its Leper ditia-l&Q 

 carapace with non-overlapping valves, the surface of which is smooth 

 and rises into an obtuse prominence. An abundant fossil in the Cin- 

 cinnatian rocks of the Ohio Valley, particularly in the Eden shale. 



Occurrence. MARTINSBUEG SHALE (Eden division). Jordans Knob, 

 one and one-half miles northeast of Fort Loudon, Pennsylvania, and debris 

 on the west slope of Eickard Mountain, Washington County, Maryland. 



Collection. U. S. National Museum. 



Family BEYRICHIIDAE 



Genus DREPANELLA Ulrich 



DREPANELLA MACRA Ulrich 



Plate XLIII, Pigs. 13-15 



Drepanella macer Ulrich, 1894, Jour. Cincinnati Soc. Nat. Hist, vol. xiii, 



p. 119, pi. viii, figs. 4a-c. 

 Drepanella macro, Ulrich and Bassler, 1908, Proc. U. S. Nat. Mus., vol. xxxv, 



p. 291, fig. 17, pi. xli, figs. 12-14. 



Description. " Valves subquadrate, about 2.0 mm. long and 1.25 mm, 

 high, with the body very thin and shallow, the thickness of the entire 

 carapace at a point near the middle being only about 0.3 mm. Ventral 

 margin straight or sinuate ; ends subequal, the posterior a little the most 

 curved; postero and antero-dorsal regions angular, the angles 10 or 15 

 degrees greater than a right angle. Ventral edge slightly thickened. 

 Marginal or sickle-shaped ridge high, projecting beyond the dorsal edge, 

 running parallel with and very close to the abrupt posterior margin ; then 

 curving more rapidly than does the outline of the valve into the ventral 

 margin, it gradually increases its distance from the ventral edge, and in a 

 slightly flexuous manner traverses the valve for almost its entire 

 length, terminating at a point near the middle of the anterior margin. 

 Postero-median ridge consisting of three prominently confluent nodes, the 



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