FORAMINIFEKA OF THE MINT SPRING CALCAREOUS MARL. 

 Distribution of Foramini/era oj the Mint Spring marl and Byram marl — Continued. 



125 



DESCRIPTIONS. 



Family TEXTULARIIDAE. 



Genus TEXTTTLARIA Defrance, 1824. 



Textularia tumidulum Cushman. 



Textularia tumvhilum. Cushman, U. S. Geol. Survey 

 Prof. Paper 129, p. 89, pi. 15, figs. 1, 2a, 2b, 1922. 



Test large, elongate, compressed, thickest 

 in the central region, thence thinning toward 

 the periphery, initial end rapidly broadening 

 in the adult, the sides nearly parallel to a 

 point near the apertural end, where the 

 breadth of the test is often reduced; chambers 

 numerous, in the adult about three times as 

 wide as high, and often the last-formed 

 chamber in old-age specimens somewhat dis- 

 tinctly set off from the others, the inner por- 

 tion of each chamber much thicker than the 

 other portions and in the rapid decrease in 

 thickness often leaving a channel running 

 lengthwise of the test between this central 

 tumid area and the gradually sloping outer 

 portion, usually well marked in adult speci- 

 mens; sutures not very distinct; wall arena- 

 ceous, but smoothly finished. Length 2.5 

 millimeters or less. 



This is the most common species of Textu- 

 laria in the Mint Spring marl, occurring at the 

 type station (6452, Mint Spring Bayou, Vicks- 

 burg. Miss.) and also at the following stations: 



6447,6448. Glass Bayou, Vicksburg, Miss. 

 6451. Mint Spring Bayou, Vicksburg, Miss. 

 7671. "Brown's Cave," Leaf River, Miss. 

 32333°— 22 10 



There is a considerable variation in rela- 

 tive length and breadth in the two forms of 

 the species, the megalospheric form being 

 usually broader and shorter, the microspheric 

 form narrower but longer. The species was 

 originally described from specimens obtained 

 in the Byram marl at Byram, Miss. 



Textularia mississippiensis Cushman. 



Textularia mississippienm Cushman, U. S. Geol. Survey 

 Frof. Paper 129, p. 90, pi. 14, fig. 4, 1922. 



Test elongate, fairly broad, thickest in the 

 middle, thence thinning toward the periphery, 

 in end view biconvex, central portion curved; 

 chambers rather low and broad , especially in the 

 early stages, becoming higher in the adult and 

 often less broad so that the later chambers in 

 the adult make a test less wide than at earlier 

 stages; sutures covered by a coarsely arena- 

 ceous layer meeting in the center and at the 

 periphery, leaving the central portion of each 

 chamber uncovered; periphery irregular, not 

 definitely or regularly spinose; chamber walls 

 smooth and finely perforate. Length 0.40 to 

 0.75 millimeter. 



This species, which was originally described 

 from specimens obtained in the Byram marl at 

 Byram, Miss, occurs at all six stations of the 

 Mint Spring marl, as follows : 



6447, 6448. Glass Bayou, Vicksburg, Miss. 

 6451, 6452. Mint Spring Bayou, Vicksburg, Miss. 

 6647. (Tiickaaawhay River 1 J miles southwest of Boice, 

 Miss. 

 7671. "Brown's C«,ve," Leaf River, Atiss. 



