768 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



calcified (fig. 12) ; they are generally empty and appear white in tangential (fig. 11) 

 and longitudinal sections (fig. 15). The interstices disappear when the section 

 passes rigorously through the point of tangency (fig. 15). 



The function of the tergopores is evidently zoarial, but we are totally ignorant 

 of their nature. 



Affinities. This species much resembles Idmonea pertusa Eeuss, 1847, in its 

 basal lamella, and in the fossils, it is difficult to separate them. It differs from it 

 in its frontal, the fascicles of which are close together and not spread out from 

 the median line. 



It differs from Idmonea reticulaia Eeuss, 1869, in the very different nature of 

 its tergopores, and from Pleuronea fusiformis in the exterior polygonal form of 

 its tergopores and in their larger diameter. 



Occurrence. Claibornian (Gosport sand) : One mile southwest of Eockville, 

 Clarke County, Alabama (rare). 



Lower Jacksonian (Moodys marl) : Jackson, Mississippi (common). 



Middle Jacksonian : Bich Hill 5 j miles southeast of Knoxville. Crawford 

 County, Georgia (very rare). 



Upper Jacksonian (Ocala limestone) : Old Factory, about \\ miles above 

 Bainbridge, Georgia (very rare). 



Vicksburgian (Eed Bluff clay) : One-quarter mile west of Woodwards, Wayne 

 County, Mississippi (rare). 



Vicksburgian (Marianna limestone) : Vicksburg, Mississippi (lower bed, 

 rare). 



Cotypes. Cat. No. 65432, U.S.N.M. 



PLEURONEA FUSIFORMIS, new species. 



Plate 161, figs. 3, 4. 



Description. The zoarium is free, bifurcated, idmoneiform. The bundles are 

 salient, transverse, alternate on each side of the median axis, and formed of four 

 to five zooecia. The tubes are little visible; the orifice is rectangular and the 

 peristome is thin. The basal lamella is convex and bears fusiform tergopores. 

 The ovicell is large, globular, salient; the oeciostome is adjacent to a bundle and 

 subterminal. 



Distance between the fascicles 0.36 mm. 



Width of the fascicles 0.10 mm. 



Zoarial width 0.50-0.60 mm. 



Dimensions of the tergopores 0.04-0.08 mm. 



Affinities. This species is the American representative of Idmonea reticulata 

 Eeuss, 1869, of the Priabonian of the Vicentin. It differs from it, however, in the 

 more elongated form of the tergopores. 



Occurrence. Vicksburgian (Marianna limestone) : Salt Mountain, 5 miles 

 south of Jackson, Alabama (very rare). 

 Holotype.Cnt. No. 65442, U.S.N.M. 



Mea-m rements. 



