20 BULLETIN" 16 5, UNITED STATES NATIONAL MUSEUM 



Variations. — The micrometric measurements are variable, the 

 largest occurring on the marginal zooecia. 



The ovicell appears under the microscope to be endozooecial, as 

 it hides the distal border of the mural rim, but by inclining the 

 preparation it is easy to see the latter attenuated and the orifice of 

 the ovicell placed above the distal septula. In a dissection, the 

 cicatrix left by the ovicell is quite visible on the distal cryptocyst. 

 The figured specimen contains two calcified cells. 



Occurrence. — Vincentown limesand : Common at Vincentown, N.J., 

 and at Noxontown Millpond and 2 miles southwest of Odessa, Del. 



Geological distribution. — Bryozoan beds at base of Aquia (Eocene) , 

 Upper Marlboro, Md. 



Plesiotypes.— U.S.N. M. Nos. 73872, 73873. 



Genus ALDERINA Norman, 1903 



ALDERINA RUSTICA D'Orbigny, 1852 



Plate 3, Figures 3, 4 



1852. Membranipora rustica D'Orbigny, Paleontologie francaise, terrains 



Cretaces, p. 558. pi. 729, figs. 21-22. 

 1900. Membranipora rustioa Canu, Bull. Soc. geol. France, ser. 3, vol. 28, p. 355. 



Description. — The zoarium encrusts fragments of shells and 

 Bryozoa. The zooecia are distinct, separated by a furrow, elongated, 

 elliptical ; the mural rim is very thin, regular, very finely granulated. 

 The opesium is of the same form as the zooecium. The ovicell is 

 hyperstomial, not closed by the operculum, globular, transverse, often 

 carinated longitudinally. 



Measurements. — 



„ . \ho = 0.5 mm. „ \Lz= 0.©-0.7 mm. 



Opesium], AO Zooecium {, no 



^ [Z<9 = 0.3 mm. \l.z = 0.3-0.35 mm. 



22 zooecia in 4 sq. mm. 



Affinities. — The micrometric measurements remain within those 

 given by Canu, 1900, for Membranipora rustica D'Orbigny, 1852. 

 These are variable on the French species, but they appear more 

 regular here, although they are larger in specimens from Vin- 

 centown as given above and especially in the specimen from 

 Noxontown. 



By inclining the preparation it is easy to verify that the mural 

 rim is complete under the ovicell, which cannot then be closed by 

 the operculum. Dissection confirms this observation. The dorsal 

 pellicle of the cells is very thin. As in the French specimens, the 

 ovicell frequently deforms the opesium of the distal zooecium. 



Occurrence. — Vincentown limesand : Rare at Vincentown and 

 near Blackwoodstown, N.J., and at Noxontown Millpond and 2 

 miles southwest of Odessa, Del. 



