90 University of Texas Bulletin 



obsolete at a point near the keel, leaving practically no groove bordering 

 the keel. The ribs, on this ridge, have sigmoidal flexures directed for- 

 wards, while at the umbilical margin the ribs are directed backwards. 

 The keel is sharp-topped, triangular in section, and elevated above the 

 level of the lateral tubercles. The section of the volution is rectangular 

 and slightly broader dorsally. At the widest point on the volution its 

 height and breadth are in the ratio of 3 :2. The section is thus truncate- 

 cuneiform; the flanks are practically straight, the venter lightly arcuate, 

 and the dorsum has a V-shaped excavation for the reception of the next 

 inner volution. 



SCHLOENBACHIA WINTONI n. sp. 

 PI. 3, figs. 8-11 



1920: Sehloenbachia sp. M, Adkins and Winton, Univ. Texas Bull. 1945, p. 34, pi. 5, 



figs. 1-4. 

 1920: Sehloenbachia sp. M, Winton and Adkins, Univ. Texas Bull. 1931, p. 22. 



MEASUREMENTS : ( Type individual ) . 



Greatest height of last volution 34 mm. 



Greatest breadth of last volution, excluding tubercles 32 mm. 



Greatest diameter of shell . 104 mm. 



HORIZON: Upper Weno formation, shale and limestone facies, and 

 ironstone bands in the blue shale of the Red River region. Known also 

 from south-central Texas. 



LOCALITIES: 601, clay-ironstone layers in blue shale of upper part 

 of Weno formation, pit of brickyards, one and three-fourths miles south- 

 east of Gainesville, Texas (type locality) ; 604, cut of Frisco track, three- 

 fourth mile north of Union Station, Denison, Texas; 612, 618, 714, 715, 

 716, near Fort Worth, Texas ; 720, 721, near Riovista, Texas. 



DESCRIPTION: Shell discoidal, volutions thickened, umbilical wall 

 steep, passing onto the flank by a rounded curve. Venter truncate, keel 

 low with a parallel groove on each side. Flanks slightly convex between 

 the ribs. Cross-section of volution subquadrate, slightly wider dorsally 

 than ventrally. Flanks ornamented with ribs, each connected with a ven- 

 tro-marginal tubercle. These ribs are either simple or bifid. The simple 

 ribs disappear dorsally before reaching the umbilical angle. The bifid 

 ribs end dorsally in a single, very tall umbilical tubercle and ventrally 

 in two less elevated marginal tubercles. 



Visible portion of suture consists of siphonal lobe, two lateral saddles 



