702 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Variations. The zoarium is often simple and isolated (figs. 5, 6) ; it is a much 

 enlarged cone, the lower part of which is ornamented with an epitheca corrugated 

 concentrically. The germinal layer is quite large (fig. 11) ; it is wanting more 

 often on the fossils, for it is very fragile. It disappears also and probably by 

 fossilization at the junction of adjacent subcolonies (fig. 3). 



When the zoarium is aggregated (fig. 3) the lower side bears as many pedun- 

 cles as there are subcolonies (fig. -t). The germination of the subcolonies appears 

 laterally (fig. 8) or almost centrally. 



The fascicles bear two or three series of tubes, rarely more (fig. 12) and only 

 on the zoarial margins. 



The ovicell (fig. 14) is little salient; it is visible on account of the great re- 

 duction which it occasions in the projection of the fascicles. 



The median section (fig. 15) is very instructive. In the center there are some 

 closed zooecia (z. <?.). The gemmation is habitual and the tubes grow one from 

 another from their dorsal according to the usual law (right side of fig. 15). The 

 young subcolonies appear to come from the superior ramification and not the 

 dorsal of a tube (left of fig. 15). 



Affinitii'x. Our specimens are not exactly identical with the Reuss figures. 

 The fascicles appear shorter and more irregular, and we believe it useful to con- 

 sider them as a variety until comparisons can be made with typical specimens of 

 each. Neither Waters nor ourselves have yet been fortunate enough to discover 

 Reuss's species in the material from Vicentin. 



Occurrence. Middle Jacksonian (Castle Hayne limestone) : Wilmington, 

 North Carolina (very common). 



Geological distribution. Priabonian of the Vicentin (Reuss). 



Plesiotypes.C&t. No. 65343, U.S.N.M. 



MESONEA, new genus. 



Greek : me-sos, median. 



The ovicell is lobate, median, subsymmetrical. The oeciostome curves over 

 and turns downward. There are curious, lateral, porous windows. The basal sin-- 

 face is ornamented with tergopores. The fascicles are arranged symmetrically on 

 each side of the zoarial axis. Eight tentacles. 



Genotype. Mesonea (Retepora) radians Lamarck, 181G. 



Range. Priabonian-Recent. 



Harmer in 1915 held that Retepora radians was the type of the genus Crisina 

 D'Orbigny, 1850. The French paleontologist applied this term to species of 

 Idnionca having a porous, basal lamella, but Crisina normaniana D'Orbigny, 1812, 

 the first described species of the genus, shows the ovicell and we have adopted it 

 as the genotype. For Lamarck's species we create the genus Mesonea, which 

 differs from Idmonea in the presence of tergopores, in the ovicell which spreads 

 entirely between the fascicles, and in the lateral porous windows. 



