MARYLAND GEOLOGICAL SURVEY 613 



ant material from the Monmouth of Maryland bridge the gap between 

 that race of argentaria and the costate ornata of Gabb. In fact the dis- 

 tance is greater between Conrad's species and Gabb's than between Gabb's 

 and the A. forteplicata n. sp. A. ornaia has, however, much more of the 

 laminar argentaria texture, a finer and less differentiated radial sculpture 

 and a relatively stronger concentric sculpture than A . forteplicata. 



Occurrence. MONMOUTH FORMATION. Brightseat and McNeys Cor- 

 ners, Prince George's County. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, U. S. National Museum. 



Outside Distribution. Ripley Formation. Exogyra costata zone. 

 Extreme top of zone, Pataula Creek, Georgia. 



ANOMIA FORTEPLICATA n. sp. 



Plate XXXV, Figs. 7-10 



Description. Shell nacreous, moderately large, rudely circular, sub- 

 circular or irregular in outline; umbones inconspicuous, submarginal, 

 medial in position, apices obtuse ; external surface sculptured with fifteen 

 to forty cordate primary radials and between each pair of primaries one to 

 five secondary lirations of more or less unequal strength; incremental 

 sculpture over-riding the radial but not modifying it to any degree ; liga- 

 ment submarginal, attached beneath the umbone in the left valve ; hinge 

 armature not developed ; adductor and byssal scars grouped within an area 

 thinly coated Avith lime, occupying the medial dorsal half of the shell ; 

 scars brownish in color, three in number, the largest of the three the major 

 byssal scar, minor byssal scar and adductor impression being subequal and 

 ventral to the major cicatrix ; ventral margin sharply crenate in harmony 

 with the external ribbing, the plications reflected on the interior of the 

 shell in some individuals almost to the umbones ; characters of right valve 

 not known. 

 Dimensions. 



Altitude 24 mm., latitude 24.5 mm., semi-diameter 6.6 mm. 



Altitude 23 mm., latitude 17.5 mm., semi-diameter 7.5 mm. 



Altitude 12.7 mm., latitude 14.5 mm., semi-diameter 3.5 mm. 



