126 Systematic Paleoxtology — Middle Devoxian 



straight; substance of shell very tliin. In the ventral valve' a strongly 

 impressed linear indentation marks the center of the shell from the 

 vicinity of the beak more than half way to the front. Surface marked 

 by extremely fine concentric striae, and, below the center of the shell, 

 by numerous undulations, which are stronger on the middle and become 

 obsolete on the sides." Hall, 1867. 



Two specimens apparently of this species were found in the bluish 

 somewhat arenaceous shales on the bank of Evitts Creek below Wolfe ^Mill. 

 One specimen has the characteristic elliptical shape of this species, the 

 fine concentric striae and the rather strong undulations on the middle 

 portion of the anterior half of the valve. The other specimen is broken, 

 but is apparently of elliptical shape and the central part of the valve for 

 half its length is marked by a conspicuous linear indentation. 



Length, 17 mm.; width, 9 mm. 



Occurrence. — Eomney Eormatiox', Hamilton Member. East bank 

 Evitts Creek below Wolfe Mill. 



Co//ecHon-.— Maryland Geological Survey. 



LiXGULA ligea Hall ( ?) 

 Plate VIII, Fig. 6 



LinguJa ligea Hall, 1860, Thirteenth Rep. N. Y. State Cab. Nat. Hist., p. 76. 

 Lingula ligea Hall, 1S67, Pal. N. Y., vol. iv, p. 7, pi. i, fig. 2. 

 Lingula ligea Schuchert, 1897, Bull. U. S. Geol. Surv., No. 87, p. 249. 

 Lingula ligea Grabau and Shimer, 1907, N. Am. Index Fossils, vol. ii, p. 197, 

 fig. 229d. 



Description. — " Shell narrow elliptical ; length equal to twice the 

 width; sides regularly curving; extremities subequal ; margins of the 

 valves thickened. Surface marked by fine concentric striae, and by a few 

 obscure or obsolete radiating striae. The typical forms are about half 

 an inch in length and one-quarter of an inch in width." Hall, 1867. 



' In this work the well known terms ventral valve and dorsal valve are used. 

 Dr. ,J. M. Clarke and some other paleontologists in their later publications call 

 the ventral the pedicle valve and the dorsal the brachial valve. 



