130 University of Texas Bulletin 



"Corbula crassicostata, sp. nov. 



"Shell triangular-ovate, gibbous ; nearly as broad as high, shorts ; gaping 

 posteriorly by a short, conically inflated, gently truncated rostrum, which 

 is placed high above the base of the shell ; unbones placed in advance of 

 the middle, that of the right valve only moderately high arched, its sum- 

 mit obtuse ; surface ornamented with very coarse, flattish-topped, concen- 

 tric ribs, separated by abrupt, deep narrow intervals. There are seven 

 or eight of the ribs on the basal half of a right valve the same number 

 of millimeters high. 



"Measurements : Height 7.5, length 10, breadth about 7 mm. 



"Occurrence: In arenaceous limestone bands of the Kiowa shales at 

 Belvidere, Kansas ; in Nos. 2-4 of the writer's 'Belvidere Section.' 



"So far as the writer can judge from material now in hand, the similar 

 Corbula that abounds in the condition of casts and molds in Texas, presents 

 no differences of specific value from the Kansas shell above described. The 

 casts show that the pallial line is very sharply impressed." 



CORBULA BASINIFORMIS n. sp. 



PI. 9, figs. 7-24; PI. 10, figs. 7-9 



MEASUREMENTS : Type- 

 Length 17.4 mm. 



Height 12.1 mm. 



Breadth 7.7 mm. 



Difference in length of valves 2.4 mm. 



HORIZON : Blue shale and clay-ironstone layers of upper half of Weno 

 formation, Red River region, abundant; Pawpaw clay, occasional. 



LOCALITIES: 604, cut of Frisco track, three-fourths mile north of 

 Union station, Denison, Texas (type locality) ; 601, pit of brickyards one 

 and three-fourths miles southeast of Gainesville, Texas; numerous other 

 localities in Cooke and Grayson counties, Texas. Rare, as limonite stained 

 casts in the Fort Worth region. 



DESCRIPTION : Shell small, inequivalve, almost smooth, with a short 

 pointed rostrum. 



Right valve, exterior: Valve rather inflated, evenly rounded, its out- 

 line almost a truncated ellipse. As seen from directly above, the umbonal 

 angle is about 120 degrees ; the dorso-anterior margin is thereafter almost 

 straight for about one-third the greatest length of shell ; the anterior mar- 

 gin then describes an evenly rounded curve, a portion of an ellipse, which 

 continues to the middle of the ventral margin ; here the margin is more 

 nearly straight, but again curves more sharply dorsally and posteriorly, 

 and reaches the posterior (rostral) angle. This angle is 90 degrees and 

 is very slightly rounded-acuminate. The postero-dorsal margin is almost 



