368 SYSTEMATIC PALEONTOLOGY 



Modiolus ionensis n. sp. 

 Plate XCVII, Pigs. 11, 12. 



Description. — Shell small, exceedingly thin and fragile, highly perla- 

 ceous, translucent to nearly transparent, elongated, narrowed and curved, 

 moderately inflated; beak depressed, not prominent; posterior portion 

 of shell made oblique by strong arching of dorsal margin and incurving 

 cf basal margin; marginal crenulations entire except on a part of the 

 basal margin; those just anterior to the beak especially strong and almost 

 like teeth ; ligament groove very narrow, shallow and inconspicuous ; in- 

 terior of shell showing exterior radiating sculpture; exterior with broad 

 area extending from beak to emarginate base and smooth except for faint 

 concentric growth lines, this smooth area separating anterior and pos- 

 terior radially sculptured areas; radial sculptured lines crossed by 

 irregular concentric lines producing irregular granulation ; umbonal slope 

 back to posterior basal margin higldy elevated; medial smooth area 

 flattened. 



This species is more produced, much more delicate and fragile, and has 

 a much more strongly incurved basal margin than M. dalli. 



Length, 7 mm. ; height, 3 mm. ; depth, 1 mm. 



Occurrence. — Choptank Formation. Jones Wharf. 



Collection. — Maryland Geological Survey. 



Genus MODIOLARIA Beck. 

 MODIOLARIA CURTA n. sp. 



Plate XCVII, Pig. 13. 



Description. — Shell small, thin, fragile, pearly, short and compactly 

 rounded, highly vaulted ; radial sculpturing on dorsal and posterior por- 

 tions very distinct, ridges broader than interspaces and flattened some- 

 what on top; sculpturing just beneath beak distinct; from beak to mid- 

 basal margin a broad area without radial sculpturing, but with concentric 

 growth lines visible; beak high and slightly projecting; interior showing 

 external radial ridging very distinctly. 



Length, 3.8 mm. ; height, 2.9 mm. 



Occurrence. — Calvert Formation. Plum Point. 



Collection. — Cornell University. 



