556 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



ti< iiotype. Meniscopora bigibbcra Gregory, 1893. 

 Ranyc. Thanetian-Helvetian. 



MENISCOPORA SUBPLANA Ulrich, 1901. 



Plate 2, figs. 4, 5. 



1001. Leprnlia subplatia UI.KICH, Maryland Geological Survey, Eocene, p. 210. pi. 59, 

 figs. 17, 18. 



Orif/in-al description. " Zoarium, as seen in three specimens, forming a hollow 

 cylinder, composed of numerous layers, each 0.8 to 0.35 mm. in thickness, and 

 varying in diameter according to the number of layers from 7 to 13 mm. Zooecia 

 not very regularly arranged, sometimes siibovatc. at other times hexagonal or 

 subquadrate. longer than wide, the length averaging about 0.45 mm. Upper sur- 

 face nearly flat, the outline of the zooecia, in aged conditions especially, scarcely 

 distinguishable and mainly by a double row of pores which, as shown by frac- 

 tures, are the mouths of small tubes transversing the wall in a vertical direction. 

 Front wall slightly convex, perforated, the pores usually smaller than those 

 outlining the zooecia, distinctly visible on the inner surface, sometimes wanting 

 over a varying space just behind the aperture. The latter is rounded in front, 

 nearly straight behind, with the angles rounded, generally semielliptical. the 

 width and length averaging, respectively, 0.15 and 0.13 mm. Small round or 

 oval avicularia generally present. Their position is variable, though usually close 

 to the rim of the aperture. While an occasional zooecium may occur, having no 

 avicularia, as many or more will be found having one on each side of the aperture. 

 Ooecia unknown. 



Fractures dividing the zooecia vertically (fig. 4) show that the walls (side 

 and front) are traversed by minute, wavy, vertical tubuli, and that the zooecial 

 cavities are connected by two series of pores, the larger set near the bottom and 

 a row of smaller pores above the midheight. The openings of the larger set are 

 often irregularly distributed over the concave floors of the zooecia." 



Ulrich 's description is quite exact. The zoarium is multilamellar and incmsts 

 algae; the lower face, in contact with the substratum is smooth or ornamented 

 with numerous small hydrostatic tuberosities. 



In the interior, the areolar cavities are quite visible. 



The gonoecia are identical in form with the other zooecia. but they are some- 

 what larger. 



Occurrence. Lowest Eocene (Bryozoan bed at base of Aquia formation) : 

 Upper Marlboro. Maryland (not uncommon). 



MENISCOPORA ELLIPTICA, new species. 



Plate 07. figs. 17-21. 



Dexi-ri jitiini. The zoarium 1 is an Eschara form composed of two lamellae, 

 placed back to back and easily separable. The zooecia. are little distinct, elon- 

 gated, straight; the frontal somewhat convex bears some pores which are little 



