272 SYSTEMATIC PALEONTOLOGY 



anteriorly for a considerable distance. Shell-substance fibrous, im- 

 punetate." Hall and Clarke, 1893. 



Although occurring at two distinct geological horizons this interesting 

 brachiopod, when considered with the associated fossils, is highly char- 

 acteristic of each horizon. The species is so well developed at the top of 

 the Fairview formation of the Maysville group that the name Ortho- 

 rhynchula bed has been applied to these strata. In this bed the species 

 often grow to an unusual size, some examples being an inch or more in 

 length. 



Occurrence. MARTIXSBURG SHALE (Fairview division). Tuscarora 

 Mountain, one and one-half miles southeast of McConnellsburg, Pennsyl- 

 vania. Upper Trenton of Kentucky and Tennessee, Lower Maysville of 

 the Ohio Valley, Virginia, Maryland, and Pennsylvania. 

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



Genus ZYGOSPIRA Hall 



ZYGOSPIRA RECURVIROSTRIS (Hall) 



Plate XLII, Figs. 9-12 



Atrypa recurvirostris Hall, 1847, Pal. New York, vol. i, p. 140, pi. xxxiii, 



fig. 5. 

 Zygospira recurvirostris Winchell and Schuchert, 1893, Geol. Minnesota, 



vol. iii, p. 466, pi. xxxiv, figs. 38-41. 

 Zygospira recurvirostris Hall and Clarke, 1895, Pal. New York, vol. viii, 



pt. 2, pi. liv, figs. 1-6. 

 Zygospira recurvirostris Weller, 1903, Geol. Surv. New Jersey, Pal., vol. iii, 



p. 161, pi. x, figs. 23-26. 



Description. " Shell small, subcircular or longitudinally subovate in 

 outline, subglobular; surface of both valves marked by 24 to 28 rounded 

 or subangular, radiating plications, which are crossed by fine, concentric 

 lines of growth. Pedicle valve gibbous, with its greatest elevation near 

 the center, subcarinate near the beak, the keel becoming broader toward 

 the front and forming a rather well-defined, more or less flat-topped 

 median fold; beak small and pointed, incurved over the beak of the 

 brachial valve. Brachial valve less convex than the other, marked by a 



