Maryland Geological Survey 625 



curved, often with an interruption to this curvature caused by the pro- 

 jection of the low umbonal ridge; narrowing behind to a subattenuate 

 posterior extremity and emarginate by the posterior sinus. Postcardinal 

 slope long and oblique. Surface convex on the umbones, sloping rather 

 abruptly to the front margin ; behind, the surface is sinused by a broad, 

 low depression which brings into prominence a postmedian umbonal ridge. 

 Specimens from tlie shales and the barite replacements indicate that the 

 surface was smooth or with obscure concentric growth lines. This con- 

 dition is clearly shown in most of our figures. Only one, an incomplete 

 replacement, shows that over the posterior part of the shell the concentric 

 lines are well defined and elevated, but not to such degree as in other 

 species. On the interior, anterior and posterior part of the shell the con- 

 centric lines are well defined and elevated, but not to such degree as in 

 other species. On the interior, anterior and posterior muscular scars, with 

 thickened inner walls, are at times very sharply defined. The cardinal 

 area is broadly arched, the denticulations are all vertical and decrease in 

 size beneath the beak." Clarke, 1904. 



Length 17 mm.; height 11 mm. 



Occurrence. — Jennings Formation, Woodmont Member, Naples 

 Fauna. Williams Road, oY-2 miles east of Cumberland. 



Collection. — Maryland Geological Survey. 



Pal^oneilo crassa n. sp. 

 Plate LXT, Figs. 14, 15 

 Description. — Shell of medium size, ovate, length about 1.6 height. 

 Cardinal margin arcuate, declining posteriorly; ventral margin gently 

 curved ; anterior extremity regularly rounded ; posterior extremity nar- 

 rowly rounded. Valves convex, becoming decidedly gibbous near umbo 

 in older individuals, surface sloping abruptly towards hinge-line, more 

 gradually towards anterior end and ventral margin; very gradually to- 

 wards posterior extremity near which the cast is occasionally concave. 

 Beaks small, anterior, situated between one-fourth to one-third trans- 

 verse diameter from anterior end, elevated slightly above hinge-line. 

 Umbonal slope rounded, not defined. 

 40 



