444 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



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

 Lenuds Ferry, South Carolina (common) ; Eutaw Springs. South Carolina (very 

 common) ; Eich Hill, Crawford County, Georgia (common) ; Baldock, Barnwell 

 County, South Carolina (common) ; one-half mile southeast of Georgia Kaolin 

 Company Mine, Twiggs County. Georgia (common). 



Upper Jacksonian (Ocala limestone) : Alachua, Florida (very rare) ; west 

 bank of Sepulga River, Escambia County, Alabama (very rare) . 



Cotypes.C&t. No. G4118, U.S.N.M. 



METRADOLIUM TRANSVERSUM, new species. 



Plate 57, figs. 1-3. 



Description. The zoarium is free, bilamellar. erect; the fronds are foliaceous 

 or nearly cylindrical ; the two lamellae, back to back, are inseparable. The zooecia 

 are indistinct, elongated, and large; the frontal is convex, thick, and formed of a 

 tremocyst resting on an olocyst, with small corresponding pores in quincunx. The 

 aperture is elongated, semilunar, with a concave proximal border; the peristomice is 

 oblique, wide, transverse,' the rimule-spiramen is wide but little deep ; its form 

 and its position are irregular. The oral avicularium is small, rare, and inconstant. 



Measurements. Apertura (^#=0.20mm. . rZs=0.80mm. 



(interior) IZa=0.17mm. }ls=QAQmm. 



Peristomice ]7)pe=0.15 mm., 

 (exterior) I lpe= 0.1 8-0.20 mm. 



Variations. On well-preserved specimens the tremopores are placed at the 

 bottom of small sulci. These tremopores are small, numerous, regularly arranged 

 in quincunx; they are easily altered by fossilization. The peristomice is very 

 irregular; the rimule is often placed quite laterally (fig. 2). and it is replaced 

 on the proximal border by a salient convexity, which augments still more the trans- 

 verse aspect of the peristomice. In old zooecia the rimule disappears, the peri- 

 stomice becomes orbicular and deep ; the species is then unrecognizable. 



Affinities. This species differs from Metradoliwn farvmmulatum in the in- 

 constance of its rimule-spiramen, its large micrometric dimensions (LsO.SO and 

 not 0.60 mm.), and in the absence of zooecia with spiramen. It differs from 

 Metradolium grande in its much smaller rimule, its smaller peristomice (lpe=0.20 

 and not 0.25 mm.), and its more numerous and smaller tremopores. 



It differs from Metradolinm sulciferum in its less deep and more transitory 

 sulci, in its very small rimule-spiramen, and the absence of the largo oral avicu- 

 larium. 



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

 North Carolina (very common). 



Upper Jacksonian (Ocala limestone) : Chipola River, east of Marianna, Jack- 

 son County, Florida (common). 



Jacksonian (Zeuglodon zone) : Shubuta. Mississippi (very rare). 



Ootypes.Czt. No. 64120, U.S.N.M. 



