MARYLAXD GEOLOGICAL SURVEY 397 



Length, 11.5 mm. ; height, 6 mm. ; diameter, 2.3 mm. 

 Occurrence. — Calvert Formation. Plum Point. 

 Collections. — Maryland Geological Surve}', Johns Hopkins University, 

 U. S. ISTational Museum. 



Leda concentric a (Say). 

 Plate CVIEI, Figs. 1, 2. 



Nucnlu coKcentrica Say, 1824, Jour. Acad. Nat. Pliila., vol. iv, 1st ser., p. 141. 

 Ifucula eoncentrica Say, 1881, Anier. Concli., pi. xii. 



Nucula eoncentrica Conrad, 1845, Fossils of the Medial Tertiary, p. 57, pi. xxx, fii>:. 3. 

 Nucula eborea Conrad, 1846, Proc. Acad. Nat. Sci. Phila., vol. iii, p. 34, pi. i, fig. 4. 

 Not Yoldia eborea Conrad, 1860, Jour. Acad. Nat. Sci. Phila., 2nd ser., vol. iv, 



p. 295, pi. xlvii, fig. 26; nor Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. 



xiv, p. .581 ; nor Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 5. 

 Nucula eoncentrica Conrad, 1863, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 581. 

 Nucula eoncentrica Meek, 1864, Miocene Check List, Smith. Misc. Coll. (183), p. 5. 

 Leda eoncentrica Dall, 1898, Trans. Wagner Free Inst. Sci., vol. iii, pt. iv, i). 588. 



Description. — " Transversely elongate-suhovate, rostrated, concentri- 

 cally striated. 



" Shell convex; rostrum considerably narrowed towards the tip : surface 

 concentrically striated with numerous, regular, equidistant, rounded 

 lines: healis rather behind the middle: ligament margin a little concave: 

 series of teeth angulated at the beaks .... 



" The regularly striated surface gives this shell a very pretty appear- 

 ance. In outline it has some resemblance to the rostrata." Say, 1824. 



Length, 6 mm.; height, 4 mm.; diameter, 1.1 mm. 



Occurrence. — St. Mary's Formation. St. Mary's County (Say) ; 

 Pocomoke City at a depth of 53 to 75 feet in a well boring where it may 

 be later than Miocene. 



Collections. — Maryland Geological Survey, Johns Hopkins LTniversity, 

 Wagner Free Institute of Science. 



Genus YOLDIA Moller. 



Yoldia L^ VIS (Say). 

 Plate CVIII, Figs. 3, 4. 



Nucula Uevis Say, 1824, Jour. Acad. Nat. Sci. Phila., vol. iv, 1st ser., p. 141, pi. x, 



fig. 5. 

 Nucula hevis Say, 1831, Amer. Conch., pi. xii. 



