540 Systematic Paleontology 



In general outline and character of the sculpture this form suggests the 

 much smaller Nemodon eufaulensis of Gabb; however, the relatively high, 

 rhomboidally grooved hinge area militates against its reference to that 

 genus and makes clear its affinities with the true Area. The type is unique 

 and has been described merely because it is so well characterized and 

 because it occurs in an area where the Cretaceous bivalves are preserved 

 only in the form of casts. 



Occurrence. — Matawan Formation. Camp U £ T, opposite Post 192, 

 Chesapeake and Delaware Canal, Delaware. 



Collection. — Maryland Geological Survey. 



Genus GLYCYMERIS da Costa 

 [Brit. Conch., 1778, p. 170] 



Type. — Area glycymeris Linne. 



Shell heavy, equivalve, equilateral or subequilateral, suborbicular ; beaks 

 almost straight, only very slightly incurved; hinge margin arcuate, set 

 Math two series of strong transverse teeth which are progressively obliter- 

 ated during growth by the subsidence of the cardinal area ; exterior sur- 

 face of valves concentrically or radially striate ; margins crenulate within ; 

 adductor scars subequal ; pallial line simple or very slightly sinuous. 



The genus originated in the Cretaceous, culminated in the Miocene and 

 is represented to-day by about eighty species, widely distributed in the 

 shallower waters of the warm and temperate seas. 



Glycymeris mortoni (Conrad) 



? Pectunculus australis Morton, 1834, Syn. Org. Rem. Cret. Group, U. S., 



p. 64. (Not P. australis Quoy, 1833.) 

 ? Pectunculus subaustralis d'Orbigny, 1850, Prodrome de Paleontologie, 



vol. ii, p. 243, no. 667. 

 f Axinwa subaustralis Gabb, 1862, Proc. Acad. Nat. Sci. Phila., for 1861, 



p. 365. 

 ? Axincra subaustralis Meek, 1864, Check List Inv. Fossils, N. A., Cret. and 



Jur., p. 8. 



Etymology: y\v K vs, sweet; v-epis, part. 



