MARYLAND GEOLOGICAL SURVEY 345 



Description. — " Suborbiciilar, with about twenty-five convex ribs, and 

 wrinkled across; inner margin crenate. 



''Beaks nearly central, a little prominent, curved backward: ribs 

 granulated on the umbones, and transversely wrinkled near the base, 

 convex: apices somewhat prominent beyond the general curve of the 

 shell : inner margin and edge crenate : cardinal teetli two. 



"Length from the apex to the base four-fifths of an inch, breadth 

 nearly the same. 



" Rather proportionally longer than the decussata and more oblique." 

 Say, 1834. 



None of the Maryland specimens have as many as twenty-five ribs. 

 Those from the Calvert formation have eighteen to twenty-one, those 

 from the Choptank formation sixteen to eighteen, and those from St. 

 Mary's formation, seventeen to nineteen. They approach V. granulata, 

 therefore, in number of ribs. 



From Calvert formation, length, 16 mm.; height, 17 mm.; diameter, 

 6.5 mm. From St. Mary's River, length 26 mm.; height, 28 mm.; 

 diameter, 9.5 mm. 



Occurrence.— ^T. Mary's FoKMATioisr. Cove Point, St. Mary's River. 

 Choptank Formation. Governor Run, 2 miles south of Governor Run, 

 Flag Pond, Jones Wharf, Cuckold Creek. Calvert Formation. 

 Chesapeake Beach, 3 miles south of Chesapeake Beach, Plum Point, 

 Truman's Wharf. 



Collections. — Maryland Geological Survey, Johns Hopkins University, 

 U. S. National Museum, Academy of Natural Sciences of Philadelphia. 



Venericardia castrana n. sp. 

 Plate XCI, Figs. 11, 12. 

 Description. — Outline suborbicular, beaks acute, prominent, curved 

 forward; shell depressed or flattened; ribs twenty-four to twenty-seven, 

 finely granulated and slightly convex near the beak and without granu- 

 lations but crossed by fine concentric wrinkles or growth lines over the 

 rest of the shell; the impressed lines between the ribs distinct near the 

 beak but almost obsolete on the outer part of the shell; ribs almost per- 

 fectly flat on outer part of shell; teeth strong; muscle impressions and 

 pallial line distinct; inner margin crenated. 



