33 Amkkican East Coast Arcas 33 



"A species of Area occurs in great abundance at Vicksburg, which Lesueur obtained 

 many years since and named it, but T have forgotten the name, and know not whether 

 he published it in Europe or not. It is rhomboidal, ventricose, with rather distant ribs 

 in the right valve, slightly grooved in the middle; in the left valve ribs double and gran- 

 ulated; inner margin profoundly toothed * * *." — Conrad, 1S48. 



Dall in iSg8 named this species Lesueurt, retaining the name tnississippiensis for Con- 

 rad's Ryssoarca mississippiensis. 



Shell inequivalve with very different sculpture on the two valves; beaks incurved, 

 mesially impressed at the tip; ribs twenty-four to twenty-eight, those of the left valve 

 wider than the interspaces and divided by such a deep groove that they appear double 

 excejrt near the hinge, conspicuously beaded except on the distal parts of the posterior 

 ribs; the ribs of the right valve narrower than the interspaces and much less grooved 

 and beaded, especially near the middle of the shell; ribs square, rising from flat inter- 

 spaces; cardinal area small, wider in front of the beaks, with several grooves, some of 

 which usually do not extend in front of the beaks; hinge narrow, the teeth fine at the 

 center, larger and more oblique distally; anterior and basal margins rounded, posterior 

 end produced and rounded. 



This abundant and characteristic species from the Vicksburg beds is readily distin- 

 guished by its small size and unusual sculpture. 



Dimensions. — Lon. +6.5,-14; alt. + 2. 5,-12. 5; semidiam. 6 mm. 



Occurrence. — \'icksburgian Oligocene of Mississippi. — Dall. Oligocene of Vicksburg, 

 Mississippi. — C. U. Museum. 



Area latidentata Dall 

 Plate VII, Figures 17, 18, 19, 20- 



Scapharca (Scapliarca) latidentata Dall, Wagner Free In.st. Sci., Trans., vol. 3, pt. 4, pp. 638, 647, 

 pi. 32, fig. 15, 1898. 



"Shell small, ovate, moderately convex, with low, quite anterior, mesially sulcate, 

 prosoccElous beaks; left valve with about thirty rounded, radiating, undivided ribs, sep- 

 arated by slighth- wider interspaces, and crossed by numerous smaller concentric ridges 

 which become beadlike on the ribs and vary in prominence in different specimens; base 

 evenly arcuate, ends rounded; cardinal area narrow, impressed, smooth, with one or two 

 grooves behind the beaks, but none elsewhere; valves slightly twisted, so that the basal 

 margin is not in a single plane; line of teeth interrupted a little behind the beaks, the 

 anterior series having the anterior and posterior teeth larger and the intervening teeth 

 thinner and more closely adjacent, all nearly vertical; posterior teeth vertical, shorter, 

 the series longer, the teeth smallest proximally and regularly increasing in size towards 

 the distal end of the series, equidistant and regular; inner margin of the valve deeply 

 fluted. Lon. 18, height 11, diam. 9 mm. 



"This little shell looks a good deal like the young af Anadara aresta Dall, but has 

 the beaks less central, less prominent, and distinctly impressed mesially, giving a some- 

 what bilobed aspect to the very young." — Dall, 1898. 



