MAKYLAND GEOLOGICAL SUEVEY 753 



cycles cannot be clearly differentiated. The members of the last cycle are 

 very thin and frail. The inner edges of the principal septa are fused to 

 the columella and to adjoining septa by trabecular-like processes. There 

 is a suggestion of paliform lobes, though the upper edges of the septa are 

 too imperfect to permit positive determination of this feature. Sides of 

 septa set with small tubercles and spine-like processes, the arrangement of 

 which cannot clearly be seen in the specimen. 



There is doubt as to the mode of origin of the columella, but it appears 

 to be spongy and trabecular. 



Dimensions. Longest transverse axis at top, about 5 mm.; shortest 

 transverse axis, 2.5 mm. ; height, 4.5 mm. 



Xamed in honor of Dr. T. Wayland Vaughan. 



Occurrence. MOXMOUTH FORMATION (Exogyra costata zone). Bed of 

 small branch about seven-eighths of a mile southwest of Brightseat and 

 three-eighths of a mile south of the Sheriff road, Prince George's County. 



Collection. Maryland Geological Survey, on deposit in the U. S. 

 National Museum. 



Suborder FUNGIDA 

 Family MICRABACIIDAE 



Genus MICRABACIA Milne Edwards and Haime 

 MlCRABACIA EOTATILIS Sp. nOV. 



Plate XLIX, Figs. 1-4 



Description.- Corallum subdiscoidal ; moderately high with flat to 

 rather strongly concave base ; sides steep below, rounding evenly into the 

 subflattish top; axial depression 1.5 mm. to 2 mm. deep. 



The costse on the base are thin, sharply defined, and alternate with the 

 septa; they start with six at the center, and by successive bifurcations 

 increase to ninety-six on the periphery; they are nearly smooth and 

 increase slightly in thickness from the center to the periphery. The costae 

 are in six groups corresponding to the groups of septa. Each group starts 

 with one costa (first cycle), which bifurcates near the center to form two 

 costas (second cycle) ; these bifurcate 0.5 mm. from the center to form 



