i6i Midway Stage 47 



concentric undulations which, curving upwards in the middle of 

 the valve, form a very shallow sulcus extending from beak to 

 base; muscular impression not distinctly marked; lesser valve 

 thin, flat, circular; marked exteriorly by lines of growth; smooth 

 within, with an oval muscular impression which is submarginally 

 located. 



" This description, and the figures referred to, show the most 

 Gryphcea-VC^^ phase of this species. Other forms are less dis- 

 tinctly sulcate and carinate. ' ' 



Peculiar specimens, presumably of this species, occur i mile 

 north of Midway. They seem to have adhered most readily by 

 the posterior portion of the valve so that they became distorted. 

 In some instances the left valve appears like a half valve, z. e., 

 the valve is split from the apex to the base and glued on 

 some surface by the straight edge; or the basal anterior margin is 

 greatly produced as in Gryphaa trachyoptera White. 



Localities. — Tbxas: Brazos river, Falls Co., about i mi. above 

 the Milam Co. line or J4 mile below the Creta- 

 ceous-Tertiary contact on this river. 



Arkansas: N. W., S. E. ^, Sect. 8, i S, 13 W.; 

 Sect. 15, I S., 14 W.; Sect. 2, 3 S., 16 W.; Sect. 

 36, 2 S., 16 W. 



Tennessee: Hannah's, i^ mi. N. of Crainesville, 

 bed b; Huddleston's; McDonald's mill, 4 mi. S. 

 W. of Middleton. 



Mississippi: >^' mi. S. of Ripley; 2 mi. K. of Rip- 

 ley (?). 



Alabama: Road ^4: mi. W. of Prairie Bluff; i mi. 

 N. of P. B.; I mi. N. of Matthews' I^anding (va- 

 rietal form); ij^ mi. S. W. of Palmer's mill 

 (var.); Y^ mi. W. of Graveyard hill. 



Georgia: Chattahoochee river, near mouth of San- 

 dy creek. 



Types. — U. S. National Museum. 



PLICA TULA. 

 Plicatulaf, PI. 2, fig. 2, a. 



This strange form has been figured simply to call attention 

 to its existence so that others may seek more perfect specimens 

 and determine its true place generically and specifically. 



From Yz mile E. of S. McConnico's, near Palmer's mill, from 

 bed 18 of section on p. 31. 



