32 Palaeontographica Americana 32 



Area, probably allied somewhat to the Claibornian rhomboidella of Lea. It is subrliom- 

 boidal, very inequilateral, moderately inflated, broadly rounded ventrally, the anterior 

 and posterior sides oblique, the former rounded, the latter longer and nearly straight. 

 The beaks are rather broad, moderately elevated above the hinge-line, bisected by a 

 feeble depression which becomes obsolete ventrally. The hinge-line is straight externally, 

 broadly feebly arcuate internally, the line of teeth more than three-fourths as long as the 

 shell, the lateral teeth becoming longer and strongly oblique. The space between the 

 beaks and the hinge-line is flattened, nearly smooth except some fine, close-set parallel 

 lines of growth, but at the posterior end there are some coarser parallel and feebly oblique 

 lines. The radial ribs are 28 to 31 in number, rather coarse and separated by much less 

 than their own widths, except in the feebly depressed area radiating from the middle of 

 the beaks where they become finer and relatively much more widely separated, and gen- 

 erally with one fine intermediate rib between them in this region toward the ventral 

 margin only; the ribs also become smaller but very close- set posteriorly in the flattened 

 area toward the hinge-Hne. The surface posteriorly at an angle of about 30 degrees with 

 the hinge-line is convex, becoming rapidly decHvous and explanate to the latter. The 

 muscular scars are rather deep. Lines of growth produce feeble transverse and rather 

 widely separated nodules on the ribs generally becoming obsolete posteriorly. The 

 length of a moderately large individual of this species is 11.5 mm., the height 6 mm." — 

 Casey, 1903. 



Area deiicatula Casey 



Area deiicatula Case}-, Acad. Nat. Sci. Phila., Proc. for 1903, p. 265, 1903. 



"Occurs in the Lower Vicksburg limestone in great abundance. It may be regarded 

 as a homologue of invidiosa and is doubtless one of the smallest known members of 

 the family. It is elongate, very inequilateral, obliquely parallelogramic, moderately in- 

 flated, becoming flattened posteriorly toward the hinge-line, the latter long, thin and 

 straight, the teeth small. The space between the hinge-line and the beaks rather 

 low, flat and smooth or nearly so, narrowing very gradually porteriorly. The imibonal 

 impression, with its diminished ribs, is nearly as in invidiosa and many other species. 

 The ribs are some 28 in number, relatively moderately coarse, being generally separated 

 by their own widths, flattened. Length of a moderately large valve 6 mm., height 

 2.6-2.8 mm." — Casey, 1903. 



Area Lesueuri Dall 

 Plate VII, Figures 12, 13, 14, 15, 16 



Lesueur, Walnut Hills Fos., pi. 5, fig. 8, 1829 {Jide Dall). 



Area Mississippiciisis Conrad, Acad. Nat. Sci. Phila., Proc. for 1847, p. 294; Journ., 2d. ser., vol. 



I, p. 125, pi. 13, figs. II, 15, 1S48. 

 Not Byssoarea mississippiciisis Conrad, Acad. Nat. Sci. Phila., Journ., 2d. ser., vol. 1, p. 125, pi. 



13, fig. 32, 1848. 

 Anomalocardia Mississippiensis Conrad, Am. Journ. Conch., vol. i, p. 11, 1865. 

 Not Cucullaarca Mississippiensis Conr&A, Am. Journ, Conch., vol. i, p. 11, 1S65. 

 Scapliarca [Scap/iarca) Lesueuri Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 643, 1898. 



