ART. 6 FOEAMINIFERA : POLYMORPHINIDAE — CUSHMAN AND OZAWA 117 

 POLYMORPHINA CUSHMANI Pliunmer 



Plate 30, figures 8 a, b 



Potymorphina cushmani Plummeb, Bull. 2644, Univ. Texas, 1927, p. 125, 

 pi. 6, fig. 9; pi. 15, figs. 1 a-c. 



Test compressed, oblong, broadest at the upper half, rhomboidal in 

 end view, margins angular but not carinate; chambers elongate, 

 alternating in an entirely biserial series; sutures not depressed, 

 straight, often thickened and obscured; wall thick, ornamented in 

 the middle part of the broad faces with raised beads arranged longi- 

 tudinally from the aperture to the initial end or not more than four, 

 strong, broken costae developing independently of the sutures; 

 aperture radiate. 



Maximum length 2.60 mm. ; breadth 1.30 mm. ; thickness 0.60 mm. 



Polymorphina cushmani is one of the best defined species of the 

 genus. Its straight sutures and peculiar ornamentation are the 

 special features that will separate it from the species related to it. 



Distribution. — This species seems to be limited to the lower Eocene, 

 Midway, of the Texas region. Mrs. Plummer describes it from the base 

 of a high bluff on west side of Colorado River between the Travis- 

 Bastrop County line and the mouth of Dry Creek (Bastrop quad- 

 rangle), Tex., and 5}^ miles due south and very slightly west of 

 Littig, where the 440-foot contour cuts a northeast-southwest road 

 (Bastrop quadrangle), Texas. The specimen here figured is from 

 the station near Littig, kindly sent us by Mrs. Plummer. We also 

 have typical specimens from the Midway of Texas in our collection 

 from other Texas localities. 



Mrs. Plummer's notes on the occurrence of this species are given 

 here: 



In the Midway formation P. cushmani is most frequent in the glauconitic 

 sands and clays in the upper part of the transition zone, which in the belt 

 of outcrop northeast of the Mexia area is marked by phosphatic nodules and 

 southwest of this same area by the abundance of Venericardia bulla. In some 

 outcropping clays it is of sufficient abundance to be detected with the aid of a 

 hand lens. Because no other formation in the Texas geologic section has yielded 

 a compressed Polymorphine test bearing strong longitudinal markings, P. cush- 

 mani becomes very useful as a Midway signpost. The underlying Navarro 

 formation carries very rarely a somewhat similar large species that is much 

 smoother and possesses fewer chambers in its fullest development. 



POLYMORPHINA COMPLANATA d'Orbigny 



Plate 30, figures 9 a, b 



Polymorphina complanata d'Orbigny, Foram. Foss. Bass. Tert. Vienne, 1846, 

 p. 234, pi. 13, figs. 25-30. — H. B. Brady, Parker, and Jones, Trans. 

 Linn. Soc, vol. 27, 1870, p. 230, pi. 40, figs. 14 a, b; woodcuts f-j. 



Test rhombic in outline, much compressed, greatest breadth above 

 the middle, acute toward the initial end ; chambers elongate, slender, 



