259 I^iGNiTic Stage 67 



''Geological horizon. — Bell's Landing, section of the Lignitic. 



"A large species of this genus. It differs from any other by 

 its smooth surface, large posterior end, and faint muscular im- 

 pressions." 



Our specimen is from near the mouth of Bashi creek, in the 

 Woods bluff horizon. 



Type. — Aldrich's collecftion. 



Specimen figured. — Near the mouth of Bashi creek; Paleonto- 

 logical Museum, Cornell University. 



Corbulaaldrichi, PI. 13, figs. 12, 13, a. 



Syn. Corbula rugosa Heilp,, Proc. Acad. Nat. Sci., Phila., 1880, p. 364. 

 Corbula oniscits Heilp., Proc. Acad. Nat. Sci., Phila., 1880, p. 364. 

 Corbula gibbosa Heilp., Proc. Acad, Nat. Sci., Phila., 1880, p. 364. 

 Corbula aldt^ichi Meyer, Amer. Jour. Sci., vol. 30, p. 67, 1885. 

 Corbiila aldrichi Aid., Bull, i, Geol. Surv. Ala., p. 83, pi. i, fig. 



21, 1886. 

 Corbula rugosa Heilp., non Ivam., Proc. Acad. Nat. Sci., Phila., 

 1890, p. 401. 



Meyer's original description. — -"Rounded trigonal ; ventricose; 

 posterior side carinated ; beak small, curved anteriorly, in the 

 left valve nearly in the middle ; right valve briefly rostrated ; in 

 both valves the umbonal part is without concentric ribs, but with 

 impressed, radiating lines — the ventral part with concentric ribs. 



'' Locality . — Woods Bluff, Ala. 



' 'The radiating lines cut only the first ribs and and disappear 

 completely at the ventral part. The species is similar to Corbula 

 gibbosa Lea, but distinguished mainly by the smooth umbonal 

 part and the radiating lines." 



Heilprin has in several instances referred this species, as well 

 as Conrad's oniscus and Lea's gibbosa to C. rugosa Lam. Were 

 ones observations confined to the larger valve (right) this com- 

 mingling of different species might be excusable. C. aldrichi 

 does not always have radiating lines on the umbones nor are 

 these parts always void of concentric striation. The radiate struct- 

 ure is made visible doubtless by slight erosion. Some specimens 

 from Ozark, and 4 miles above Hamilton bluff, on the Alabama, 

 and from Hatchetigbee, have the nasute posterior, the very 

 strong lirae and in general, appear like small oniscus. But with 

 them are specimens varying to the aldrichi type, and all left 

 valves found are of the short, rotund shape of the latter species, 



