198 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



twq. The zooecia are rectangular; the opesium is anterior, elliptical, and is sur- 

 rounded by a thin mural rim projecting but little; the gymnocyst (?) is ;Kvell 

 developed and bears two symmetrical tuberosities, which represent small avicularia 

 opening laterally in the same plane as the adjacent rows; the two distal avicu- 

 laria visible in the neighborhood of the opercular valve also match those of adja- 

 cent rows. Ovicell endozooecial. 



. |Ao=0.26-0.36 mm. T \Ls=0.44 mm. 



Measurements. -Laxg* opesiaj^^^^ mm Large zooeciaj fe=a40 



Affinities. This is a very curious species, which is difficult to classify. We 

 have placed it in Nellia because of its great resemblance to Nellia appendicidata 

 Hincks, 1883, a living species from Australia, and to Farcimia articulata Ma<^- 

 Gillivray, 1895. 



It is also close to Quadricellaria ventricosa Canu, 1913, of the Girondin Lute- 

 tian of France: only the absence of a little distal crescent distinguishes it fvom 

 this European species. 



When we know the chitinous appendages of these two species perhaps it will 

 become necessary to place them in a new genus with N. appendiculata. 



There are two rows of broad zooecia opposite each other, and two rows of 

 similarly placed narrow zooecia. At the base of certain opesia, exteriorly or in- 

 teriorly, there is sometimes a radicular pore; such zooecia. therefore, bear at the 

 same time a polypide and a radicular fiber. 



As we have found this species in the three Midway localities studied, it seems to 

 be a characteristic form and is thus deserving of the name applied to it. 



Occurrence. Midwayan (Clayton limestone) : Mabelvale, near Little Rock, 

 Arkansas (very rare) ; 1 mile west of Fort Gaines, Georgia (very rare) ; Luverne, 

 Crenshaw County, Alabama (common). 



Cotypes.Ca,t. Nos. 63800, 63801, U.S.N.M. 



Genus HETEROCELLA Canu, 1907. 



1907. Heterocella CANTJ, Bryozoaires des terniins tertiares des environs de Paris, Anuales 

 de Paleontologie, vol. 2, p. 14. 



The zoarium is articulated with each segment formed of four rows of zooecia. 

 The opesia are always oblique; they are small on the converging zooecia and large 

 on the diverging ones. On the olocyst at the bottom of the zooecia there are im- 

 pressions of various forms. 



Genotype. Vincularia fragilis Defrance, 1820. 



In Europe this genus has been observed only in the French Lutetian. Its struc- 

 ture is still problematical, for no existing species is comparable to these fossil forms. 

 Some of the zooecia described by Canu as regenerated are perhaps radicular. 



HETEROCELLA VICKSBURGICA, new species. 



Plate 82, figs. 11-14. 



Description. The segments are quadrangular, straight, or slightly curved. 

 The zooecia are distinct and rectangular; the mural rim is rounded, Drojecting dis- 



