MARYLAND GEOLOGICAL SURVEY 477 



biserial manner and overlapping in such a way that while one side re- 

 mains nearly flat the opposite is more or less irregularly vaulted and 

 shows all the chambers in parallel arrangement; final segment broad 

 below, embracing, and bearing the mammillate aperture upon the anterior 

 end. Shell surface smooth; finely perforate. Polymorphina anceps 

 Eeuss, and P. proUcma var. deltoidea Keuss are probably identical with 

 this species. The same species is found in the Eocene at Woodstock, 

 Virginia. 



Occurrence. — Calvert Formation. Chesapeake Beach. 



Collection.— MsLiyUnd Geological Survey. 



Polymorphina gibba (d'Orbigny). 

 Plate CXXXTII, Fig. 4. 



GloJmlhm <,ibba d'Orbigny, 1846, Foram. Foss. Vienne, p. 227, pL xiii, figs. 13, 14. 

 Polymorphina gibba Bagg, 1901, Md. Geol. Survey, Eoceue, p. 248, pi. Ixui, tg. 12. 



Description.— Test subglobular, apex slightly produced, base obtusely 

 rounded, consisting of from two to four chambers compactly joined and 

 overlapping. The surface is smooth, unmarked by any septal con- 

 striction. Septa visible as fine oblique lines. In transverse section the 

 shell appears almost circular. The aperture is mammillate and the speci- 

 mens we have are rather small. It occurs in the Eocene of Maryland 

 but is never a common species. 



Occurrence. — Calvert Formation. Chesapeake Beach. 



Collection. — Maryland Geological Survey. 



Polymorphina lactea (Walker and Jacob). 

 Plate CXXXIII, Figs. 5, 6. 



Serpnla larlen Walker and Jacob, 1798 (flde Kanmacber's Ed.), Adams Essays, 



Microsc, p. 634, pi. xiv, fig. 4. 

 FolymorpMna lactea Bagg, 1898, Bull. Amer. Pal., No. 10, p. 31. 

 Polymorphina lactea Bagg, 1901, Md. Geol. Survey, Eocene, p. 248, pi. Ixiii, tig. 13. 



Description. — This rather common form of Polymorphina has an 

 ovate or subpyriform test, only slightly compressed and has but three or 

 four chambers with flush sutures and faint septal lines. The aperture is 

 terminal, radiate. It occurs as a fossil as early as the Jurassic and is 

 present from there on with increasing numbers. 



