782 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



not the case in all our specimens. Moreover, the micrometric measurements do not 

 appear identical, if the small drawing of Manzoni is exact. It is to be noted that 

 figure 6 represents a branch with alternated fascicles. 



A species, also very close, is Idmonea marginata D'Orbigny, 1853, of the Euro- 

 pean Senonian. If we consider, for example, figure 8, with its eight tubes to the 

 fascicle, the identity is perfect. The zooecial and zoarial dimensions are also identi- 

 cal. The only appreciable difference is that the number of the tubes to the 

 fascicle is frequently larger than in the Tertiary species. The study of bases and 

 ovicells will perhaps permit us some day to make better comparisons. 



This species differs from Idmonea arcuata in the linear form of its zoarium 

 and in the distance between the fascicles being double. It differs from Idmonea 

 sloani in its larger dimensions and in its transverse section wider than high. 



Occurrence. Middle Jacksonian: Wilmington, North Carolina (very rare); 

 near Lenuds Ferry, South Carolina (rare) ; Eutaw Springs, South Carolina (rare). 



Vicksburgian (Marianna limestone) : West bank Conecuh River, Escambia 

 County, Alabama (very common). 



Vicksburgian (Byram marl) : One-fourth mile west of Woodwards, Wayne 

 County, Alabama (rare). 



Geological distribution. Lutetian of Bavaria (Beutler) ; Auversian at Biar- 

 ritz (C'anu). 



Plesiotypes.C&t. Nos. 65355, 65356, U.S.N.M. 



IDMONEA TRIFORATA Canu, 1911. 

 Plate 161, figs. 5-24. 



1911. Idmonea triforata CANU, Les Bryozoaires tin Sud-Ouest de la France, Bulletin de la 

 Soctete g6ologlque de Prance, ser. 4, vol. 11, p. 452, pi. 8, figs. 13-14. 



Description. The zoarium is free, linear, bifurcated, with triangular trans- 

 verse section wider than high. The fascicles are very salient, irregularly spaced, 

 arranged alternately on each side of the median crest and distant from it, pro- 

 jecting beyond the zoarial margins; they are formed of three or four zoecia, the 

 last of which is turned and opens on the dorsal face and the first is isolated on 

 the young branches. The tubes are visible, long, convex; the peristome is quad- 

 rangular. The basal lamella is smooth and somewhat convex. 



Diameter of the tubes 0.20-0.24 mm. 



Distance between the fascicles 0.70-1.00 mm. 



Width of the fascicles 0.14-0.16 mm. 



Zoarial width 0.75 mm. 



Variations. This species is exceedingly irregular; the distance between the 

 fascicles has no constancy and varies from 1 to 2 times (0.60 to 1.20). On the 

 terminal branches the first zooecium of each fascicle is isolated on the median axis 

 of the zoarium (figs. 7, 8, 14, 15) and measures 0.30 mm. in diameter. On the 

 branches of the base or lower branches the fascicles are regular and complete 

 (figs. 12, 13). This double disposition is often visible on the same specimen. 



Measurements. 



