296 SYSTEMATIC PALEOXTOLOGY 



Genus ABRA Leach. 



Abra longicallus (Scacchi). 

 Plate LXXII, Figs. 9a, 9b. 



Tellina longicallus Scacchi, 1836, Notizie intorno alle Conchiglie ed a zoofiti fossili, 

 p. 16, pi. i, fig. 7. 



Description. — Shell ovate, thin, convex or vaulted; beak not promi- 

 nent; anterior and posterior sides straight, meeting at an angle; anterior 

 end broad and regularly rounded; posterior end very acutely rounded, 

 much above the line of the base and gaping ; base regularly curved ; pos- 

 terior adductor scar rounded ; anterior one elongated ; pallial sinus long 

 and irregularly curved; in right valve the lateral lamina on either side 

 rather short and bordered by a moderately deep groove; cardinals two, 

 minute; chondrophore elongated, narrow, oblique, closely grown to the 

 posterior hinge line ; exterior surface smooth. 



Length, 11.5 mm. ; height, 7.1 mm. ; diameter, 2 mm. 



Occurrence. — Choptank Formation. Jones Wharf. 



Collection. — Cornell University. 



Abra marylandica n. sp. 

 Plate LXXII, Fig. 10. 



Description. — Shell small, compact, stout, vaulted; anterior end pro- 

 duced and rounded ; posterior end shorter, more pointed ; and nearer the 

 line of the base; anterior and posterior dorsal margins nearly straight, 

 anterior one nearly parallel to the basal margin, posterior one much 

 more declining; beak not prominent, but angular; exterior polished and 

 smooth except for a few feeble concentric growth lines near the margin, 

 muscle impressions and pallial line faint, interior polished; in left valve 

 a narrow fosset directed posteriorly and close set against the posterior 

 margin ; anterior to it is a small triangular cardinal tooth, posterior to it 

 the margin is slightly raised as if into a faint lamina and slightly flaring 

 or reflexed near the beak. 



Length, 7 mm.; height, 4.5 mm.; diameter, 1.6 mm. 



Occurrence. — Calvert Formation. Plum Point. 



Collection. — Maryland Geological Survey. 



