Maryland Geological Survey 621 



Paljeoxeilo plana Hall 

 Plate LXI, Figs. 1-3 



PalcBoneilo plana Hall, 1870, Prelim. Notice Lammellibr., vol. ii, p. T. 

 Paloeoneilo plana Hall, 1885, Pal. of N. Y., vol. v, pt. i, sec. ii, p. 334, pi. 



xlviii, figs. 21-28. 

 PaJcEoneilo plana Grabau and Shinier, 1909, N. Amer. Index Foss., vol. i, 



p. 399, flg. 510. 

 Palcconeilo plana Cleland, 1911, Bull, xxi, Geol. Survey Wis., p. 104, pi. xx, 



figs. 15-16. 



Description. — Sliell below medium size, elongate-ovate, length about 

 twice height, occasionally greater. Cardinal margin curved, slightly con- 

 cave anterior to umbo, slightly convex posterior to umbo ; ventral margin 

 gently curved; anterior extremity rounded; becoming narrower towards 

 posterior extremity which is abruptly rounded. Valves convex, somewhat 

 gibbous towards umbo; cast of interior slightly concave in some speci- 

 mens towards posterior extremity. Beak small, not much elevated above 

 hinge-line, situated about one-third length from anterior extremity. Um- 

 bonal slope rounded, not distinct. Casts of interior show hinge teeth in a 

 curved line, teeth at extremities being stronger; anterior and posterior 

 muscular scars shallow; anterior scar separated from umbo by a slight 

 ridge in some shells. Surface with faint concentric lines. Test thin. 



Length 18 ram., occasionally more; height 9 mm. 



The individuals referred to this species differ in some respects from 

 those described by Hall. They are, however, probably the same species 

 although this identification is not without question. K specimen from 

 near Pratt is much more elongate than usual. This species closely re- 

 sembles P. elongata of the Chemung of Xew York. It differs in being 

 larger with beak nearer anterior extremity. It differs from P. crassa in 

 being smaller, more elongate, test thin, muscular scars shallow. 



Occurrence. — Jennings Formation, Chemung Member. National 

 Eoad west of Frostburg; Town Creek, 3228, 2391, 3969; 2 miles west of 

 Pawpaw, 2124; 21^ miles northeast of Pratt near home of Mr. Cheney ?; 

 Millstone, 2322 abundant. Parkhead Member. Town Creek, 1G79 ?, 

 1851. Woodmont Member, Ithaca Fauna. Little Orleans, 1446. 



Collection. — Maryland Geological Survev. 



