53 St. Maurice and Ci^aiborne PeIvKCypoda 53 



showing a tendeuc}- to have grooves on the distal portions of the 

 big umbonal costse. 



Senile forms become edentulous save at either extremity of 

 the hinge . 



Types— Fhila. Acad. Nat. Sci., No. 5306. 



Specimens figured . — Paleont. Mus. Cornell Univ.; Aid. Coll., 

 Johns Hopkins Univ. 



Localities. — Texas : Lee Co. ; Louisiana : St Maurice ; ^ 

 mile S. of Winona ; Hammett's Branch ; 3 miles S. E. of Ne- 

 greet ; Mississippi: Newton; Wautubbee (Aldr.). Ala. : Clai- 

 borne sands ; base of Claiborne bluff, Lisbon. 



Area vaughani Casey, PI. 22. Figs. 5, 6, 7. 



Area rhoviboidella var. Vaughan, U. S. G. S., 142 ; pi. 3, fig. 8, 1896. 



A. vanghani Casey, Proc. Acad. Nat. Sci. 1903, p. 265. 



A. vaughani Sheldon, Palseontogr. Amer., vol. i, 1916, p. 31, pi. 7, 

 figs. II. 

 Casey^ s description . — A species quite common in the Lower Claiborne 

 at St. Maurice, La., and allied somewhat iorhoniboidella Lea. It attains a 

 length of more than 22 mm with a height of 12 mm or more, obliquely rhom- 

 boidal, moderatel)' inequilateral, rounded anteriorly and posteriorly and 

 broadly rounded ventrally. It is moderately inflated, the radiating concav- 

 ity at the middle of the umbones almost obsolete and Imving merely slightlj- 

 wider intervals between the ribs, the latter 41-43 in number. The hinge- 

 line is long and straight, the teeth becoming larger and very oblique later- 

 ally but well developed throughout, with their sides finely ribbed, giving to 

 each tooth a bipectinate appearance. The area under the beak is ample and 

 broadly divaricately striate. This species differs from rhomboidella in its 

 much larger size, more numerous ribs, rounded ventral edge and many other 

 characters, and may be named vaughani. A fair illustration of it was given 

 by Mr. Vaughan (Bull. Geol. Surv. 142, PI. Ill, fig. 8), in whose honor it is 

 named. A modification of the true rhomboidella, but still smaller in size, 

 also occurs sparingly at St. Maurice. 



Dr. Sheldon has already corrected the misconception as re- 

 gards comparative size of the species mentioned. 



This is seemingly a direct off-shoot from rhomboidella with a 

 more arcuate ventral margin, more even ribbing, more oblique 

 form and comparatively thicker shell substance. There are in- 

 termediate forms, however, very difficult of classification. 



7>/^.— U. S. Nat. Museum? 



Specimens figured. — Paleont. Mus., Cornell Univ. 



