S2Q CRETACEOUS PALEONTOLOGY. 



Description. — The dimensions of a right valve are : length, 56 

 mm. ; height, 3 1 mm. Shell subelliptical in outline, the beaks 

 small, subcentral in position, scarcely elevated above the hinge- 

 line, pointing posteriorly, fissured. Antero^-cardinal margin 

 straight and horizontal in front of the beak, curving downward 

 anteriorly; anterior margin broadly rounding from the cardinal 

 to the basal margins; basal margin curving upward in front 

 and behind, nearly straight in the middle, subparallel with the 

 ■dorsal margin; posterior margin most produced near the cardi- 

 nal line, curving broadly tO' the basal margin and more sharply 

 to the cardinal extremity; post-cardinal margin concave just 

 behind the beaks, becoming nearly straight posteriorly. Valves 

 depressed convex, a little gaping behind. Surface of the shell 

 in front of the beaks^ marked by rather strong, more or less 

 irregular concentric undulations, and by fine, more or less irreg- 

 ular lines of growth ; posterior half of the shell marked by more 

 or less inconspicuous concentric markings, and by about 10 or 

 12 narrow, angular, radiating costse, the most anterior of which 

 extends nearly vertically downward from the beak to the ventral 

 margin, being slightly bowed forward; back of this is a rather 

 broad smooth space beyond which the costse reappear, the inter- 

 vals between them gradually becoming wider posteriorly, the 

 most posterior one reaching the posterior margin of the shell 

 near the middle, leaving a smooth area for some distance below 

 the cardinal border. 



Remarks. — This species, originally described! from Tippah 

 County, Mississippi, has not. been previously recognized in New 

 Jersey. It occurs in the recent collections of the Survey in both 

 the Woodbury clay and the Wenonah sand. In the original de- 

 scription of the species the anterior and posterior extremities of 

 the shell were reversed. There was also published at the same 

 time with the definition of this species, the descriptions of two 

 others, A. postsulcaita and A. papyria, but the types of both of 

 these have apparently been lost or destroyed. However, both 

 are probably only variations of A. anteradiata and are not 

 worthy of recoignition as distinct species. The species is an 

 abundant one at the original locality in the Ripley beds of Tip- 



