322 Systematic Paleontology 



Some specimens from Tonoloway are larger than those described by 

 Hall and have much coarser striae. They are questionably referred to 

 this species. It is cited by Hall as coming from the lower Helderberg 

 rocks of Cumberland. 



Length about 1 cm. ; width 1.8 cm. 



Occurrence. — Helderberg Formation, Keyser Mejiber. Devil's 

 Backbone, Viaduct Cumberland, Cash Valley, Tonoloway, Maryland; 

 Keyser, West Virginia. 



Collection. — Maryland Geological Survey. 



[Maynard.] 



Strophonella leavenworthana (Hall) 

 Plate LIX, Figs. 6, 7 



Stropliomena (Strophodonta) leavenworthana Hall, 1857, Tenth Ann. Rept. 



N. Y. State Cab. Nat. Hist., p. 53. 

 Strophonella leavenworthana Hall and Clarke, 1892, Nat. Hist. N. Y., Pal., 



vol. viii, pt. i, p. 292, pi. xii, figs. G-9. 



Description. — " Shell subsemicircular, about three-fourths as long as 

 wide, contracted below the extremities of the hinge; cardinal border 

 sloping slightly from the beak : ventral valve flattened in the middle and 

 cardinal margins, so as to form a semicircular inclined plane ascending 

 from the hinge to beyond the middle of the shell ; the front and lateral 

 margins abruptly inflected, giving a deep concavity to the whole valve: 

 dorsal valve flattened or slightly concave in the umbonal and central 

 regions, very convex towards the front and lateral margins: hinge-line 

 equal to the greatest width of the shell, crenulated; area linear, vertically 

 striated; foramen small, triangular, closed in full-grown individuals. 

 Surface marked by fine, obscure, closely arranged, radiating strise, crossed 

 on the depressed part of the valves by small regular concentric wrinkles." 

 Hall, 1857. 



None attain the large size of New York examples, but otherwise are 

 indistinguishable. The species is readily distinguished from S. pimctu- 

 lifera by the much finer radial stria3 and the more decided concavo-convex 

 curvature of the valves. 



Length 3.5 cm. ; width 4.5 cm. 



