ART. 20 THE GENUS SIPHONINA AND OTHER GENERA CUSHMAN" 5 



tion, slightly inflated on the ventral side; sutures distinct, strongly 

 oblique, slightly curved, somewhat limbate on the dorsal side, on the 

 ventral side nearly radial, depressed; wall smooth, very distinctly 

 perforate; aperture elongate, narrowly elliptical, occupying the 

 whole height of the chamber, with a distinct lip but no definite neck. 



Diameter 0.35 mm.; thickness 0.15 mm. 



Holotype.—{C^t. No. 369617, U.S.N.M.) from the Claiborne, Lis- 

 bon formation, 1 mile north of Washitubbee Station, N. O. and N. E. 

 Railroad, Clarke County, Miss., collected by E. N. Lowe and C. 

 Wythe Cooke. 



It also occurs in the Lisbon formation at bridge over Falling 

 Creek, 6 miles south of Quitman, Clarke County, Miss., and cut 

 on Alabama and Vicksburg Railroad, 3^4 miles east of Newton, 

 Newton County, Miss., and south bank of Tombigbee River at bend 

 in river % mile below Lock No. 1 and about 1 mile above St. Stephens 

 Bluff, Washington County, Ala. 



This is a very much smoother species than the preceding with a 

 very slight development of the keel. It is a forerunner of such 

 species as Siphonin^t jacksonensis Cushman and Applin, 



SIPHONINA JACKSONENSIS Cushman and Applin 



Plate 1, figs. 6 d-c 



Siphwima jachsonensis Cushman and Applin, Bull. Amer. Assoc. Petr. Geol., 

 vol. 10, 1926, p. 180, pi. 9, figs. 20-23. 



Test of medium size for the genus, nearly circular, nearly equally 

 biconvex, much compressed, periphery angled, sharply acute, deli- 

 cately serrate, lobulate ; chambers usually five in the last-formed coil, 

 the last ones inflated somewhat on both sides; sutures slightly de- 

 pressed, oblique and curved on the dorsal side, nearly radial below, 

 the umbilical region with clear shell material; wall slightly spinose 

 throughout ; aperture narrowly elliptical, nearly the whole height of 

 the chamber, with a distinctly thickened lip but no definite neck. 



Diameter up to 0.55 mm. ; thickness 0.18 mm. 



This species was originally described from the Jackson Eocene, 1 

 miles east of DiboU, Angelina County, Tex. It has proved to be a 

 common species now known from the Upper Eocene of Louisiana, 

 Mississippi, Alabama, and North Carolina. It also occurs in the 

 Alazan clay of Mexico collected by Dr. T. Wayland Vaughan on 

 Rio Tuxpan, 200 meters above the mouth of the Rio Pantepec, Vera 

 Cruz, Mexico. 



SIPHONINA JACKSONENSIS Cnshman and Applin. var. LIMBOSA Cushman, new variety 



Plate 4, fig. 2 



Tests differing from the typical in the very limbate sutures and 

 finer perforations of the wall. 



