G26 Systematic Paleoxtology — UrrER Devonian 



The shell becomes thick and iiiassive in older individuals. Surface 

 smooth with faint concentric strige. Cast of interior shows a broad hinge- 

 plate bearing long teeth which are in one line, teeth coarse at extremities of 

 hinge, fine beneath umbo. Anterior and posterior muscular scars deep ; 

 umbo bearing a number of umbonal pits ; pallial line distinct. 



Length of larger individuals 25 mm. ; height 16 mm. or slightly greater 

 in some cases; attaining a thickness of 14 mm. 



This species is characterized by its thick test and the lack of a defined 

 umbonal ridge and sulcus. In the latter respect it resembles P. elongata 

 of the Chemung of New York but it is less elongate than that species. 



Occurrence. — Jennings Formation, Chemung Member. National 

 Eoad west of Frostburg; Towti Creek, 3453 cf., 3538 common, 3584 

 abundant, 3593 common; west of Tonoloway Eidge near Pennsylvania- 

 Man'land state line opposite school house. 



Collection. — Maryland Geological Survey. 



Genus LEDA Schumacher 

 LeDA cf. DIVEESA Hall 



Plate LXI, Figs. 16, 17 



Leda diverse Hall, 1885, Pal. of N. Y., vol. v, pt. i, sec. ii, p. 329, pi. Ixvli, 



figs. 31-37. 

 Leda diversa Grabau and Shimer, 1909, N. Amer. Index Foss., vol. 1, p. 401, 



fig. 511. 



Description. — Shell small, falciform ; length twice or a little more than 

 twice width. Cardinal margin convex, post-umbonal portion concave 

 upwardly, anterior portion slightly convex, declining from beak; ventral 

 margin gently curved ; posterior end smaller than anterior end, attenuate, 

 curved upwards. Valve convex. Umbo situated about one-third length 

 from anterior end. Umbonal ridge extending from beak to posterior 

 extremity; surface of shell sloping abruptly from it to hinge-lino, round- 

 ing gently to ventral margin. Surface ornamentation unknown. 



Length 10-12 mm.; height 3-5 mm. 



The specimens figured ditfer considerably in form and may not all be- 

 long to the same species. Their proportions suggest L. diversa of the Ham- 



