134 University of Texas Bulletin 



convexity in its posterior one-third. The valve is distinctly rotund and 

 elevated. 



The ornamentation consists of 12 coarse rounded concentric ribs, and 

 a number of fine growth lines in the umbonal region; the. ventral half of 

 the height contains nine of the coarse ribs. These ribs turn dorsally along 

 the anterior end of the rostrum and just posterior to the oblique shallow 

 groove, making an angle of 95 degrees to 100 degrees. The ribs near 

 this angle bear each about four or five fine growth lines. The edges of the 

 ribs appear as thin slightly imbricated and overlapping lamellae. Dorsal 

 to the angle, the rostrum is conically inflated, the width of the fold in- 

 creasing postero-ventrally and at the posterior end occupying the whole 

 height of the rostrum. Dorsal to the inflation is a narrow concurrent 

 and slightly divergent depression. The rostrum is half the height of the 

 shell and is very close to the ventral margin. The ribs are unbranched and 

 continuous from the anterior to the posterior ends of the valve. They are 

 elevated with rather sharply rounded tops and are separated by plane 

 bottomed, vertical-sided valleys whose width is one-sixth that of a rib. 



Remarks: The following species of Corbula are to be found in the 

 literature on the Comanchean : C. pikensis Hill (Trinity division) ; and 

 C. crassicostata Cragin, Kiowa, Kansas, and (by implication) in the 

 "ochreous shell-conglomerate of the Denison beds, Denison, Texas." 

 C. basiniformis is distinguishable from the other species mentioned by its 

 relatively unornamented surface and its geniculate margin. C. littoralis 

 is distinguished from the others by its few coarse elevated and broad ribs ; 

 C. wenoensis is distinguished from C. littoralis by its smaller size, its 

 different and less elongate form, its greater number of ribs, the more dor- 

 sal position of its rostrum, the shape and relative height and position of 

 the rostrum, and by the internal characters as described. 



CYPRIMERIA WASHITAENSIS n. *p. 



PI. 9, figs. 1-6 



Type 



MEASUREMENTS: PL 9, fig. 1 PL 9, fig. 4 PL 9,.fig. 2 



Height 52.0 52.0 76 



Length 58.5 59.0 77+ 



Breadth 15.0 17.5 25 



HORIZON: Weno formation, upper and middle thirds, shale facies. 



LOCALITIES : 604, cut of St. Louis and San Francisco Railway, one 

 mile north of the Union Station, Denison, Texas (type locality) ; 601, pit 

 of brickyards, three-fourths mile southeast of Gainesville, Texas. 



