15 American East Coast Arcas 15 



"Shell oblong, compressed, thin, with very numerous radiating granulated striae; beaks 

 not prominent; base much contracted or emarginate anterior to the middle; posterior 

 side dilated, the superior margin very oblique and emarginate; extremity angulated, 

 and situated nearer to the line of the hinge than to that of the base; cardinal teeth 

 minute, except towards the extremities of the cardinal line, where they are comparatively 

 very large and oblique ; inner margin entire. 



"Locality. Cliffs of Calvert, Md. * * *." — Conrad, 1840. 



Ribs not varying conspicuously over the shell, often alternating with finer ribs an- 

 teriorly, smoother and usually double posteriorly; posterior part of the shell two-angled 

 or broadly rounded; cardinal area with numerous v-shaped grooves; form of shell often 

 irregular. This species lacks the sharp umbonal ridge of A. aiculloides. 



Bvssoatra ttian'landica Lea, Acad. Nat. Sci. Phila., Proc. for 1848, p. 97, and Area 

 marylandicus Heilprin, Acad. Nat. Sci. Phila., Proc. for 1881, p. 451, are misprints for 

 this species. 



Dimensions. — Lon. + i7,-36; alt. +6, -30; semidiam. 14 mm. 



Occurrence. — Oligocene of the Ballast Point silex beds, Tampa Bay, the lower (Chip- 

 ola) bed at Alimi Bluff, the Chipola marl of the Chipola River, Florida; older Miocene 

 of Jericho, Cumberland County, New Jersey; Middle Miocene of Plum Point, Calvert 

 Cliffs, and Centreville, Maryland. Possibly also in the Jacksonian. — Dall. Calvert Mi- 

 ocene of three miles west of Centreville, Plum Point. Centreville, Maryland. — Glenn. 

 Oligocene of Bailey's Ferry, Florida. — C. U. Museum. 



Area arcula Heilprin 



Plate III, Figures 8, 9 



Area arcula Heilprin, Wagner Free Inst. Sci., Trans., vol. i, p. iiS. pi. i6, fig. 65, 1887. 

 Barhatia (Calloarca) arcula Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 624, pi. 33, fig. 

 4, 189S. 



"Shell moderately elongated, sharply angulated on the posterior slope, the dorsal 

 and ventral borders nearly straight and parallel with one another; dorsal (hinge) line 

 not much more than half the length of shell; anterior border projecting foru-ard basally; 

 posterior border acutely angulated with the base; beaks anterior, not very prominent, 

 nor very widely separated; ligamental area narrow; teeth almost obsolete in the middle 

 of the hinge-line, becoming oblique toward either extremity; interior of shell deep; ex- 

 ternal surface closely ribbed, the ribs strongly imbricated by the rugose lines of growth; 

 ribs most prominent on the posterior slope, where they are echinated. 



"Length, 1.7 inch; height to top of imibo, 1 inch." — Heilprin. 1887. 



"Shell subovate, thin, inflated, the beaks low and prosogyrous; the cardinal area 

 narrow and very closely and minutely furrowed longitudinally, the furrows showing a 

 slight angle behind the beaks; sculpture of close set, fine radial ribs, rather regularly 

 imbricated at successive lines of growth; on the posterior dorsal slope are six or eight 

 nodulous larger ribs; the beaks are situated a little behind the anterior third; byssal 

 foramen narrow, ver}' anterior; hinge with a few large v-shaped teeth at the ends, the 



