MARYLAND GEOLOGICAL SURVEY 235 



Description. Shell small, calcareo-corneous, circular in outline and 

 cone-shaped in form ; 2 to 3 mm. in height. Pedicle valve conical with the 

 height greater than the length. Apex usually broken, but showing evi- 

 dence of the external opening of the sipho. Extending from the apex to 

 the posterior margin is a shallow furrow increasing in width downward. 

 The posterior wall of the shell conforms to the curvature of the rest of 

 the surface in small specimens, but this area becomes distinctly flattened 

 in larger examples, as in Acrotreta. Surface covered with sharp con- 

 centric striae curving slightly upward as they cross the foraminal groove. 



In casts of the interior a strong apical callosity marking the probable 

 position of the foramen is produced anteriorly into a short, sharp ridge, 

 on either side of which lie two other ridges, with evidence of a third on the 

 lateral slopes. 



The highly conical form of this calcareo-corneous shell and the numer- 

 ous radiating ridges on the ventral interior readily distinguish this 

 interesting brachiopod. 



Occurrence. MARTINSBURG SHALE (Sinuites bed). Chambersburg, 

 Pennsylvania, and Strasburg, Virginia. Trenton limestone, Trenton 

 Falls, Xew York. 



Collection. U. S. National Museum. 



Family TREMATIDAE 



Genus SGHIZOGRANIA Hall and Whitfield 



SCHIZOCRANIA FILOSA (Hall) 



Plate LII, Figs. 8, 9 



OrUcula ? filosa Hall, 1847, Pal. New York, vol. i, p. 99, pi. xxx, fig. 9. 

 Schizocrania fllosa Hall and Whitfield, 1875, Pal. Ohio, vol. ii, p. 73, pi. i, 



figs. 12-15. 

 Schizocrania filosa Weller, 1903, Geol. Surv. New Jersey, Pal., vol. iii, p. 146, 



pi. ix, figs. 3, 4. 



Description. " Shell orbicular or subovate, the beak of the free or 

 brachial valve projecting slightly beyond the limits of the circle, giving 

 a somewhat greater diameter along the median line than in a transverse 

 direction. Pedicle or attached valve discoid, very thin, deeply and broadly 



