American East Coast Arc as 



Dimensions. — Lon. + 11,-30; alt. +3,-16; semidiam. 11 mm. 

 Occurrence. — Lignitic Eocene of Hatchetigbee, Alabama. 

 Type. — C. U. Museum. 



Area subprotracta Heilprin 



Plate I, Figure 4 



Byssoarca protracta Conrad, .\cad. Nat. Sci. Phil., Proc. for 1S47, p. 295, 1848; Journ., 2d. ser., 



vol. I, p. 126, pi. 13, fig. 36, 1848. 

 Not Area protracta Rogers, Am. Phil. Soc, Trans., vol. 5, p. 332, 1837; vol. 6, pi. 26, Cg. 5, 1839. 

 Navicula protracta Conrad, Acad. Nat. Sci. Phila., Proc. for 1854, p. 29. 

 Area subprotracta Heilprin, Acad. Nat. Sci. Phila., Proc. for 1881, p. 449, 1882. 



"Trapezoidal, elongated, with numerous radiating lines, some of which are double, 

 and others alternated in size and finely crenulated; dorsal margin parallel with the base; 

 anterior margin tnmcated, posterior a little concave, oblique and very acutely 

 rounded or subangular; basal margin slightly contracted; hinge long, rectilinear, 

 very regular and gradually increasing in width towards the extremities from the apex; 

 cardinal area wide, depressed concave, with a few fine, impressed, angular lines. 



Length I'^/i; height i^ in. nearly. 



"A pretty species of which I found one valve only." — Conrad, 1848. 



Occurrence. — "Newer Eocene [Oligocene] of Mississippi. — Conrad. 



Area paratina Dall 



Plate I, Figures 5, 6, 7 



Area fiaratiiia Dall, Wagm-r Free Inst. Sci., Trans., vol. 3, pt. 4, p. 621, pi. 33, fig. 14, 189S. 



"Shell elongated, not very thick or high, not much distorted, but with a variable 

 byssal gape, inequilateral, the beaks at or near the anterior fourth; moderately alate in 

 front and behind: beaks low, pointed, not inflated, their apices slightly prosogyrate ; 

 cardinal area long, narrow, lozenge-shaped, flattish, with longitudinal strije, the site of 

 the resilium marked on each valve by two grooves forming a small triangle, within which 

 are traces of the inception of other grooves; sculpture chiefly of fine radial riblets over- 

 running and somewhat imbricated by not prominent lines of growth; the radials which 

 end on the margin of the byssal foramen are perceptibly finer than the rest, those on the 

 posterior dorsal slope are more or less fasciculated, the ends of the fascicles dentating 

 the posterior margin; on the dorsal anterior part the riblets increase somewhat in size, 

 but are not fasciculated; the dorsal border in front is anterior to the rest of the margin; 

 between the dorsal posterior extreme and the ventral posterior angle there is often an 

 irregular, but not deep emargination; the borders of the byssal foramen are irregularly 

 emarginate; interior smooth, the margin denticulated by the sculpture except at the 

 foramen; hinge-line straight, minutely denticulate; the teeth in the center smaller, those 

 towards the ends inclined outward slightly, above, and a little larger; there are about 

 twenty three anterior and forty posterior teeth, with no marked hiatus between the 

 series. Lon. of shell 28, alt. of hinge-line 8.5, of beaks 10, diam. at the umbonal part 

 10 mm. It is quite possible that the shell grows to a considerably larger size. 



