MARYLAND GEOLOGICAL SURVEY. 311 



Another point of difference from T. bidorsata is that the umbilicus is 

 smaller and less abrupt and the volutions more rounded on each side and 

 therefore elongate, reniform in cross-section. In the Eden shales, speci- 

 mens of this species average 20 mm. in height. 



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

 one and one-half miles northeast of Fort Loudon; Tuscarora Mountain, 

 two and one-half miles southeast of McConnellsburg ; and Cowan Gap, 

 five miles northeast of McConnellsburg. 



Collection. U. S, National Museum. 



Family CYRTOLITIDAE 



Genus CYRTOLITINA Ulrich 



CYRTOLITINA NITIDULA (Ulrich) 



Plate L, Figs. 17-18 



Cyrtolites nitidulus Ulrich, 1879, Jour. Cincinnati Soc. Nat. Hist, vol. ii, 



p. 12, pi. vii, figs. 7, 7a. 

 Cyrtolitina nitidula Ulrich, 1897, Geol. Minnesota, Pal., vol. iii, pt. 2, p. 866, 



pi. Ixii, figs. 53-55. 



Description." Shell small, 6 to 8 mm. in diameter ; volutions about 

 two, rapidly increasing in size, the outer embracing quite a half of the 

 inner ; dorsum blunt, thick, flattened in casts ; sides gently convex to the 

 edge of the umbilicus into which they descend at first rather abruptly, 

 then gently, the ventral part spreading saddle-like over the inner volu- 

 tion. Aperture subcordate, notched below; outer lip rather broadly and 

 deeply emarginated. Umbilicus about 3.5 mm. wide in a specimen 8 mm. 

 in diameter, narrowly rounded at the edge. Surface of casts with distinct, 

 subregular, retrally curved, transverse striae, averaging about five in 

 2 mm. on the sides and back. The striae continue over and are quite 

 distinct and curved on the flattened dorsum or slit-band. On the latter 

 some very fine revolving lines, about four in 1 mm., occur on the sides of 

 the volutions. Greatest diameter of a large specimen 8.3 mm. ; width of 

 aperture 5.0 mm.; height of same 5.0 mm."' Ulrich, 1897. 



