MARYLAND GEOLOGICAL SURVEY 683 



sinus linguiform and obliquely ascending almost but not quite to the 

 median horizontal. 



Aphrodina tippana Conrad is one of the most widely distributed and 

 most characteristic species of the Exogyra costata zone. Weller has deter- 

 mined some casts from the Matawan of New Jersey by this name, but they 

 seem to show at least a subspecific difference in the shorter, relatively 

 higher outline and the less produced, more broadly rounded posterior end. 



Occurrence. MONMOUTH FORMATION. Brightseat, Prince George's 

 County. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, U. S. National Museum. 



Outside Distribution. Magothy Formation. New Jersey. Ripley 

 Formation. Exogyra costata zone, Union, Tippah and Alcorn counties, 

 Mississippi; Georgia; Eufaula, Alabama. Extreme top of zone, Chatta- 

 hoochee River, Georgia. 



Genus LEGUMEN Conrad 

 [Jour. Acad. Nat. Sci., Phila., 2d ser., vol. iii, 1858, p. 325] 



Type. Lcgumen ellipticus Conrad = L. planulatum Conrad. 



" Shell equivalve, very inequilateral, flattened ; hinge with two very 

 slender teeth in the right valve under the beak, and one posterior, very 

 oblique, prominent, lamelliform tooth." Conrad, 1858. 



Legumen like the associated Leptosolen occurs most frequently in the 

 form of casts, but it is readily differentiated from the latter by the rela- 

 tively greater altitude, the ellipsoidal rather than cylindrical outline, and 

 particularly by the absence of a sulcus across the umbones. 



The genus, though quite abundant locally, has a restricted distribution 

 within the Cretaceous. 



A. Altitude of shell not more than half the latitude Legumen planulatum 



B. Altitude of shell equal to or greater than half the latitude 



Legumen carolinense 



Etymology: Legumen, a bean. 

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