MARYLAND GEOLOGICAL SURVEY 637 



ing the posterior sixth of the shell smooth; incremental sculpture over- 

 running the radials and minutely nodulating them in the umbonal 

 region, imbricating them away from the umbones ; characters of interior 

 not known. 



Liopistha protexia Conrad is abundant and widespread in the Upper 

 Cretaceous of the East Coast and Gulf. For that reason and because its 

 stratigraphic distribution is apparently restricted it has been used by 

 Stephenson 1 as the guide fossil for the so-called Liopistha protexta sub- 

 zone which he has traced through Georgia, Alabama and Mississippi. 



Occurrence. MONMOUTH FORMATION. Bohemia Mills, Cecil County; 

 Millersville, Anne Arundel County; Brightseat, Brooks estate near Seat 

 Pleasant, railroad cut 1 mile west of Seat Pleasant, 2 miles south of Oxon 

 Hill, Prince George's County, Maryland. EANCOCAS FORMATION. 

 Noxontown Pond, Delaware. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey, U. S. National Museum. 



Outside Distribution. Matawan Formation. ? Wenonah sand, New 

 Jersey. Monmouth Formation. Navesink marl, Eed Bank sand and 

 Tinton beds, New Jersey. Peedee Formation. North and South Caro- 

 lina. Ripley Formation. Exogyra costata zone, Eufaula, Alabama; 

 Chickasaw, Lee, Pontotoc, Union, Tippah and Alcorn counties, Mississippi. 

 Extreme top of zone, Pataula Creek, Georgia; Chattahoochee River, Ala- 

 bama. Selma Formation. Exogyra costata zone, Wilcox County, Ala- 

 bama ; east-central Mississippi. 



LIOPISTHA ALTERNATA Weller 



Liopistha alternata Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 

 p. 527, pi. Iviii, figs. 7-9. 



Description. " The dimensions of an average left valve are : Length 

 22 mm., height 15.5 mm., convexity 7 mm. Shell, exclusive of the pro- 

 jecting beaks, subelliptical in outline. Beaks central, or in some speci- 

 mens apparently a little back of the center, their apices pointed, elevated 



1 Prof. Paper, U. S. Geol. Survey, No. 81. 



