Maryland Geological Survey 417 



species attains the largest growth — upward of 80 mm. in width. This 

 size is as large as the largest New York examples, and they are more con- 

 vex, with a decidedly wider and deeper ventral sinus. These specimens 

 represent the typical form of S. arenosus, while the smaller ones, so 

 common in the " sand pockets " about Cumberland, are a distinct variety 

 easily recognized by the shallow valves with their almost obsolete fold and 

 sinus. 



Occurrence. — Oriskany Formatiox, Shriver Member. A single 

 small specimen was found in the Lower Oriskany at North Branch. 

 RiDGELY Member. Allegany and Washington counties, Maryland; 

 Keyser and Moorefield, West Virginia; Eock Enon Springs, Alexandria, 

 Virginia. It is also found in the drift about Washington and Alexandria. 



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

 American Museum of Natural History. 



Spirifer concinnus Hall 

 Plate LXXII, Figs. 2, 3 



Spirifer concinna Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., 



p. 60, figs. 1-3 on p. 61. 

 Spirifer concinnus Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 200, pi. xxv, 



flgs. 2g-2i; pi. xxviii, fig. 7 (not figs. 2a-2f of pi. xxv, probably a new 



species of the 8. cyclopterus section). 



Description. — " Shell semicircular or semielliptical ; extremities 

 rounded; valves almost equally convex: ventral valve gibbous towards 

 the beak; beak more or less elevated above the hinge-line, and abruptly 

 incurved at the apex; mesial sinus subangidar, and produced into an 

 angular extension which is much elevated, and sometimes slightly in- 

 curved in front: dorsal valve very convex in the center; beak scarcely in- 

 curved; mesial elevation obtusely angular; hinge-line equal to or a little 

 less than the width of the shell ; area of medium size, well defined, and 

 extending to the ex-tremities of the hinge-line. Surface marked by from 

 twelve to fourteen rounded, little elevated, simple costse on each side of 

 the lobe and mesial sinus [marked by radial lines of minute interrupted 

 granules]." Hall, 1857. 



