MARYLAND GEOLOGICAL SURVEY 231 



the species cannot be considered typical. Paterula, which differs from 

 Leptobolus in having the inner margins of the valves thickened, must also 

 be considered in determinating its final generic position. 



Compared with other species of Leptobolus, L. ovalis is distinguished 

 at once by its larger size, more elongated, oval shape, more rounded beak 

 and less clearly marked interior. 



Occurrence. MARTINSBURG SHALE (Sinuites bed). Many localities in 

 the Chambersburg and Mercersburg quadrangles of Pennsylvania and in 

 the southern extension of the same strata into Maryland. The figured 

 specimens are from the locality two miles northeast of Kauffman, Penn- 

 sylvania. 



Collections. Maryland Geological Survey, U. S. National Museum. 



LEPTOBOLUS INSIGNIS Hall 

 Plate LIT, Fig. 13 



Leptobolus insignis Hall, 1871, Fossils from Hudson River Group, p. 3, pi. iii, 

 fig. 17 (Twenty-fourth Kept. New York State Cab. Nat. Hist., p. 227, 

 pi. vii, fig. 17). 



Leptobolus insignis Hall and Clarke, 1892, Pal. New York, vol. viii, pt. i, 

 p. 74, pi. iii, figs. 1-6. 



Description. Shell semiphosphatic, minute, 1.50-2.00 mm. in length, 

 fragile, orbicular, with a scarcely pointed beak. Valves subcircular, 

 regularly convex and marked with concentric lines of growth on the 

 exterior surface. Ventral valve with a distinct pedicle groove and an 

 elevated subquadrate muscular area on its interior. The dorsal valve is 

 somewhat thickened on the cardinal margin and bears slightly elevated, 

 trifid muscular impressions. The internal surface with radiating striae 

 separates this species from other forms of the genus. 



Occurrence. MARTINSBURG SHALE (Corynoides bed). Chambers- 

 burg, Pennsylvania, and Williamsport, Maryland. Utica shale of New 

 York, Canada, and the Ohio Valley. 



Collections. Maryland Geological Survey, TJ. S. National Museum. 



