482 SYSTEMATIC PALEONTOLOGY 



Occurrence. — St, Mary's Formation. St. Mary's Eiver. Choptank 

 Formation, Jones Wharf, Governor Eun. 

 Collection. — Maryland Geological Survey. 



Genus SPIROLOCULINA d'Orbigny. 

 In the genus SpirolocuUna the segments are arranged in one plane 

 and the chambers extend the entire length of the shell in alternating 

 series with the aperture successively changing from end to end as the 

 form enlarges. This fact of the appearance of all the chambers upon 

 both sides of the shell serves to distinguish the genus from Miliolina 

 types of two or more overlapping chambers and the Biloculina type in 

 which only two chambers ever appear externally. The genus is subject 

 to considerable variation and the symmetry of the shell is not always 

 followed. The genus inhabits shallow waters of tropical and temperate 

 zones and is rarely met with at depths beyond 600 fathoms. As a fossil 

 the genus is known from the several portions of the Lias and it has been 

 recognized in almost every succeeding formation. 



Spiroloculina grata Terquem. 

 Plate CXXXIII, Fig. 14. 



Spiroloculina grata Terquem, 1878, Mem. Soc. geol. France, ser. iii, vol. i, p. 55, 

 pi. X, figs. 14-15. 



Description. — Test broadly oval or almost circular in outline; 

 chambers, four, Milioline, covered with definite striations upon their outer 

 surface which is the chief characteristic of the species. The umbilical 

 region is depressed and the outer chambers are somewhat enlarged 

 towards their margin, suggesting a thickening of the shell as well as an 

 increase in size. The surface striations are in our specimen nearly paral- 

 lel to the several chambers, but Brady mentions the fact that these are 

 sometimes oblique and often irregular. While in typical forms the 

 aperture ends in an elongated neck. In our specimen it appears broken 

 so that this feature is not apparent. 



The only specimen we have of this peculiar tropical form is from 

 the sands at Chesapeake Beach, where the Foraminifera are best devel- 

 oped in the Maryland beds. It is a coral reef species in existing seas 

 and is a shallow water form. It is not known before the middle Ter- 

 tiary. 



