798 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Diameter of the peristome 0.12 mm. 



Diameter of the apertura 0.08 mm. 



Distance between the perist.unes 0.40 mm. 



Separation of the peristomes 0.40 mm. 



Variations. The peristome is not alwaj's salient (figs. 4, 5), which reduces the 

 diameter of the apertura (fig. 7). The frontal nervi disappear easily in fossiliza- 

 tion (figs. 6, 7). The two large vacuoles adjacent to the apertura are very constant, 

 but some others may appear. Generally the more vacuoles there are, the smaller 

 they are. The apertures are grouped quite rarely in transversal lines (fig. 9). 



The dorsal face is quite variable. Figure 10 illustrates the most frequent 

 occurrence. The nervi become sometimes smaller and more numerous (fig. 11) ; 

 rarely they become wider at the expense of. the attenuated sulci (fig. 12). 



The tangential section of the frontal always shows three or four vacuoles 

 perforating the zoarium (fig. 13) the structure of which is composed of much 

 crowded elements (fig. 14). 



On the dorsal the vacuoles are smaller (fig. 15) and their obliquity is easilv 

 visible (fig. 16). The removal of the dorsal face by prolonged abrasion shows the 

 usual lozenge-shaped interior: the cavity mentioned by Hennig, 1910, therefore, 

 does not exist (fig. 17). 



The vacuoles radiate in everj' direction and are rarely parallel. Many succes- 

 sive longitudinal sections are necessary, then, in order to comprehend the zoarial 

 structure. Figure 23 shows the great complexity of the dorsal plexus, figure 24, 

 the frontal vacuoles; figure 25, the dorsal vacuoles; while figure 26 illustrates the 

 lamellar and squamous structure of the walls. 



Affinities. In the number of frontal vacuoles this species is close to Hornera 

 frondiculata Lamouroux, 1821, but it differs from this recent species in its orbicular 

 and nonelliptical orifice and in its ovicell not provided with reticulations. 



It differs from Hornera striata Milne-Edwards, 1836, in having more than 

 two frontal vacuoles and in its dorsal vacuoles being often larger. 



It differs from Hornera porosa Stoliczka. 1862. in its much smaller dorsaJ 

 vacuoles and in its orbicular and nonelliptical orifice. 



This species is found in all Jacksonian deep-water localities. 



Occurrence. Middle Jacksonian: Wilmington, North Carolina, (very com- 

 mon) ; 3^ miles south of Perry, Georgia (common) ; Baldock, Barnwell County, 

 South Carolina (rare) ; 18 miles west of Wrightsville, Johnson County, Georgia 

 (common) ; 12 miles southeast of Marshallville, Georgia (very common) ; 17 miles 

 northeast of Hawkinsville, Georgia (common) ; K miles southeast of Lilly, Dooly 

 County, Georgia (very common); 3-} miles north of Grovania, Georgia; one-half 

 mile southeast of Georgia Kaolin Co. mine, Twiggs County, Georgia (common). 



Upper Jacksonian (Ocala limestone) : Old factory, about 1| miles above Bain- 

 bridge, Georgia (very rare) ; Alachua. Florida (common) ; west bank Sepulga 

 River, Escambia County, Alabama (very common). 



Cotypes. Cat. Nos. 65242, 65312, U.S.N.M. 



