Weno and Pawpaw Formations 127 



HORIZON : Middle and Upper Weno shale and clay-ironstone. 



Locality of figured material : 604, cut of St. Louis and San Francisco 

 track,- three-fourths mile north of the Union Station, Denison, Texas ; the 

 species occurs throughout the Red River region, and is abundant at locality 

 601, pit of brickyards, near Gainesville, Texas. 



CORBULA WENOENSIS n. .p. 



PI. 10, figs. 1-4 



MEASUREMENTS: I II III 



Length 10.6 11.6 11.2 



Breadth (one valve) __. 3.8 4.4 4.0 



Height 7.7 8.1 8.0 



Length of rostrum 2.0 2.5 2.5 



HORIZON: Weno formation, upper half, clay and ironstone phase, 

 abundant; Pawpaw clay, rare. Abundant in the Red River region. 



LOCALITIES: 604, near Denison, Texas (type locality); 601, near 

 Gainesville, Texas. 



Shell small, inequivalve, concentrically ribbed with a truncated rostrum. 



Right valve, exterior: Form a very irregular quadrilateral ; size small. 

 Viewed directly from above, the valve is roughly pear shaped and consists of 

 a very inflated rotund body and a narrowed and depressed posterior siphon 

 tube or rostrum. The umbonal margin is roughly the arc of a circle whose 

 diameter equals the height of the shell. This border passes by a sharp- 

 pointed curve of 120 degrees into the anterior border, which is almost a 

 straight line making an angle of about 45 degrees with the dorso-ventral 

 axis of the valve. The anterior border passes into the ventral border by a 

 sharply rounded curve which is approximately the arc of a circle one-half 

 the diameter of the dorso-ventral dimension (height) of the shell ; the anter- 

 ior and ventral borders if extended would meet at an angle of about 55 de- 

 grees. The ventral border is very slightly convex and this approximates 

 a straight line through one-half the greatest length of the shell, where it 

 is perpendicular to the dorso-ventral axis. A little anterior to its middle 

 there is slight concavity which involves the lower two or three ribs of 

 the shell. The ventral border now curves upward and posteriorly, reach- 

 ing the narrowed siphon tube. 



The snout-shaped siphon tube lies opposite the middle one-third of the 

 height of the shell and is roughly a right angled isosceles triangle whose 

 hypotenuse is the line of attachment to the body of the valve. This line 

 of attachment is a narrow constricted or depressed zone which notches 



