218 SYSTEMATIC PALEOXTOLOGY 



line of the raised margin, in the larger size and different form of the 

 apertnre, and the grauo-lineate marking of the whole surface. 



Occurrence. — Aquia Foematio^'. 2 miles below^Potomac Creek. 



Collection. — Mar3dand Geological Survey. 



Family CRIBRILINIDAE. 



Genus CRIBRILINA Hincks. 

 CKIBEILIlNrA MODESTA n. Sp. 



Plate LX, Figs. 12, 13. 



Description. — Zoarium forming a delicate parasitic patch upon foreign 

 bodies. Zooecia ovate, not very regularly arranged, about 0.4 mm. in 

 length and 0.28 mm. wide, bordered by a thin rim. Front wall gently 

 convex, usually with six (five to seven) radiating and transverse furrows, 

 each with two or three pores, on each side, and a central, flattened, ovate 

 or triangular space, including five or six similar pores placed in obscure 

 transverse furrows. Apertures rounded, prominent, oblique, the pos- 

 terior edge highest and often thickened in its central portion. Small 

 avicularian cells occur near or attached to one part or another of the 

 apertural rim of most zooecia, generally one to each, rarely two. Where 

 three zooecia join there is usually a small open space (? vibracular cell). 

 Ooecia cucullate, moderately arched. 



I could find none among the numerous species of Crilrilina and the 

 related, if not congeneric, forms referred to Escliaripora, Semiescliari- 

 pora and Beptescliaripora by d'Orbigny that exactly matches the fossil 

 above described. It is distinguished from nearly all of them by the 

 cribrose, central space on the front wall, and the prominent rounded 

 aperture. 



Occurrence. — Aquia Foematiox. Upper Marlboro. 



Collection. — Maryland Geological Survey. 



Ceibeilina ceassula n. sp. 



Plate LX, Fig. 14. 



Description. — Zoarium encrusting. Zooecia oblong quadrate or hexa- 

 gonal, irregularly arranged, with a heavy, strongly elevated margin. 



