MARYLAND GEOLOGICAL SURVEY 97 



to a variable degree; their septa are unusually fine, and are denticulated 

 on their lower sides ; the interspaces are filled up solidly. The alee have 

 their summits very oblique, with their sutural edges nearly or quite 

 smooth. In most of the fossil specimens (Tab. I, fig. 4b, r), and slightly 

 in some of the recent specimens, the surface of the sheath presents an 

 unusual character, in a narrow longitudinal, slightly raised border, 

 running along the sutures, on the rostral side of each suture. 



Basis thin, porose; sometimes with an underlaying cancellated layer." 

 The best development of this species in Maryland, both in abundance 

 and in size of the individuals, is in the Choptank formation. The 

 Calvert forms are dwarfs and the exterior of the shell is strongly 

 corrugated. The form described by Lea as B. finchii was a young 

 individual. B. proteus Conrad is a typical concavus as was long ago 

 established by Darwin, whose monograph is based largely on Maryland 

 material. 



The individuals in the Choptank and St. Mary's formations grow in 

 clusters on Pectens and other large Molluscan shells. 



This species occurs in the Miocene of the entire Atlantic Coast. It 

 is very abundant in the Miocene and Pliocene of Europe. It is interest- 

 ing to note that Darwin regards it as recent only in the Pacific, where 

 it occurs on the coasts of California, South America, the Philippines, 

 and Australia. 



Basal diameter, ?3 mm. ; height, 52 mm. 



Occurrence.— St. Mary^s Formation. St. Mary's Eiver, Cove Point, 

 Pocdmoke City (well 53-63 feet deep). Choptank Formation. Jones 

 Wharf, Pawpaw Point, Flag Pond, Turner, St. Leonards Creek, Cor- 

 dova, Governor Run, 2 miles south of Governor Run, Greensboro, Sand 

 Hill, Peach Blossom Creek, Trappe Landing, Dover Bridge. Calvert 

 Formation. Plum Point, Truman's Wharf, Chesapeake Beach, 3 miles 

 south of Chesapeake Beach. 



Collectiom.—M.aTjlsind Geological Survey, Johns Hopkins Univer- 

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

 Wagner Free Institute of Science, Cornell University. 



