16 University of Texas Bulletin. 



slightly forward, situated anteriorly; shell closed anteriorly, 

 gaping posteriorly. Surface marked by lines of growth, which 

 vary considerably in size. 



.This shell resembles very closely, H. vulgar is Shattuck, but 

 differs from it in the curve of the dorsal and ventral margins, 

 the expansion of the posterior, the greater proportional thickness 

 of the shell, and the ornamentation. 



Locality. Shoal Creek, Austin, Texas. From the top of the 

 formation downward, about six feet. 



PACHYMYIDAE. 



Genus PACHYMYA Sowerby. 



PACHYMYA AUSTINENSIS VAR. BUDAENSIS n. var. 



PI. V: PL VI. 



Pachymya austinensis Shumard, 1859, Trans. Acad. Sci. St. 



Louis, Vol. I, pp. 604-605. 

 Pachymya austinensis White, 1879, Eleventh Ann. Kept. U. S. 



Geol. and Geog. Surv. Terr., p. 298, PI. 8, figs. 1, a, b; 



PI. 5, figs. 7, a, b. 

 Pachymya austinensis Hill, 1889, Geol. Surv. Texas, Bull. No. 



4, p. 15. 

 Pachymya austinensis Shattuck, 1903, U. S. Geol. Surv., Bull. 



205, p. 26. 



Dimensions. Length, about 15cm. ; breadth, about 9cm. ; 

 thickness, about 5.5cm. 



Description. Shell large, heavy, gibbose; beaks anterior, in- 

 curved, approximate; umbonal slope angulated from the beaks 

 to the posterior extremity; anterior margin short, narrowly 

 rounded ; posterior margin truncate, narrowly rounded to angu- 

 late below ; ventral margin concave in the middle, more rounded 

 anteriorly than posteriorly; dorsal margin nearly straight, sub- 

 parallel to the ventral; sides, with a depression extending from 

 below the beaks, obliquely backward and downward t6 the ven- 

 tral margin; surface ornamented with strong, concentric lines 

 of growh, crossed by granulate lines radiating from the beaks. 

 This shell is very closely related to P. austinensis Shum. and 

 may be identical with it, but the Buda type is much higher pos- 

 teriorly, and not so greatly angulated on the umbonal slope. 



