NORTH AMERICAN EARLY TERTIARY BRYOZOA. 767 



The longitudinal section (fig. 18) shows us larger and less entangled tergo- 

 pores than in Pleuronea alveolata; they are also longer and more oblique. 



Affinities. When the tergopores are arranged in longitudinal series this species 

 presents the aspect of Pleuronen fibrotw ; but it is distinguished from it by its much 

 larger orifice and the greater separation of the fascicles. 



It differs from Plan-oxen nlreolntn in the greater separation of the fascicles 

 and in the different position of the ovicell, and from Idmonea reticulntn Reuss, 

 1869, in the very different form of the orifice of the tergopores. 



Occurrence. Claibornian (Gosport sand) : One mile south of Rockville. 

 Clarke County, Alabama (rare). 



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



Middle Jacksonian : One-half mile southeast of Georgia Kaolin Company's mine, 

 Twiggs County, Georgia (rare) : 12 miles southeast of Marshallville, Georgia 

 (rare) ; Baldock. Barnwell County, South Carolina (very rare). 



Jacksonian (Zeiiglodon zone) : Bluff on south side of Suck Creek, Clarke 

 County, Mississippi; Shubuta, Mississippi (common). 



Vicksburgian (Marianna limestone) : Salt Mountain, 5 miles south of Jackson, 

 Alabama (rare) ; Vicksburg, Mississippi (rare) ; Murder Creek, east of Castlebury, 

 Conecuh County, Alabama (very rare). 



Geological distribution. Helvetian of Italy (Neviani) ; Tortonian of Austria- 

 Hungary (Manzoni) and Italy (Neviani); Astian of England (Busk). 



Plesiotypcs.G&t. Nos. 65266, 65267, U.S.N.M. 



PLEURONEA SUBPERTUSA, new species. 



Plate 113, figs. 6-15. 



Description. The zoarium is free, branched, with suborbicular section, 

 idmoneiform. The fascicles are quite oblique, opposite, and reunite on the zoarial 

 axis. The tubes are salient, with the maximum number of six to a fascicle; they 

 are flat and are separated by a salient thread. The basal lamella bears tergopores, 

 the diameter of which is perceptibly equal to that of the tubes. 



(Diameter of the peristomes 0.10 mm. 



' [Distance between the fascicles _ 0.20-0.28 mm. 



Vni'tations. The species is rarely well preserved; it must have frequented 

 violent currents or agitated waters. The basal lamella with its tergopores is easily 

 detached from the anterior portion of the zoarium (fig 10). 



The tergopores are deprived of polypide; their diameter is that of the tubes. 

 They grow on the dorsal of the tubes in variable number; they diverge at first 

 superiorly and then curve abruptly perpendicularly to the zoarial axis, thus form- 

 ing a right angle (fig. 15). Their walls are thickened, a fact which is perfectly 

 visible in tangential sections (fig. 12) ; they are orbicular in the interior and 

 polygonal at the exterior. 



Each tergopore has only one point of tangency with each of the other tergo- 

 pores which surround it. The interstices between the nonadjacent walls are rarely 



