30 Paleaontographica Americana 30 



or pinkish, especially near the beaks; the posterior part shows two ridges running from 

 the beaks, one, as in ^. //w7^/a, to the angle with the ventral margin, the other to the 

 angle in the posterior margin near the hinge. The margin is crenulated in the younger 

 shells, but only feebly so in the old specimens. 



Dall states that Area trapezia Desh., from West Mexico, also belongs in A^tJ^/za. 

 Specimens in the Newcomb collection labelled Scapharca trapezia Desh., which corre- 

 spond with Reeve's figure and description do not belong to this group, howe^•er. 



Subgenus Scapharca Gray 

 Section Scapharca 



"Group of A. inequivahis Brug. {Scapharca (Gray, 1847) Adams, 1858.] 



"Moderately thin, elongate-ovate, wdth prosocoelous beaks, rather narrow cardinal 

 area, not wholly covered by the ligament and usually with concentric resiliary lozenge- 

 like grooving; tooth series uninterrupted, the teeth small, similar, somewhat larger and 

 more oblique distally, the right valve smaller, the sculpture on the two valves usually 

 similar or not markedlj^ discrepant; the epidermis much as in Argitia." — Dall. 



Area rhomboidella Lea 



Plate VII, Figures 6, 7, 8, 9, 10 



Area rhomboidella Lea, Contributions to Geol., p. 74, pi. 2, fig. 52, 1833. 



Anomolocardia rhomboidella Conrad, Smith. Misc. Coll., Eocene and Oligocene Checklist, p. 4, 



1866. 

 Area rhomboidella de Gregorio, Faune Eoc. Alabama, p. 196, pi. 24, fig. 28, i8go. 

 Area (CueuUaarca) cucuUoides de Gregorio, 1. c, p. 195, pi. 24, figs. 17-20. 

 Area rhomboidella Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 625, 1898. 



"Description. Shell rhomboidal, very inequilateral, compressed at base, longitudi- 

 nally and closely ribbed; substance of the shell thin; beaks small, pointed; ribs about 

 thirtj'-three, obsoletely tuberculated on the anterior portion; teeth lamellar, oblique; 

 cicatrices scarcely perceptible; cavity of the shell rather shallow; margin crenulate. 



"Diam * =>= * Length .2, Breadth 7-ioths, of an inch. 



"Observations. This pretty little species forms, by its parallel sides, nearly a perfect 

 rhomboid. It has some resemblance to the ce/ilcnaria of Say, which is described bj^ him, 

 as well as Mr. Conrad, as being 'subrhomboidal.' The figures, however, are both trape- 

 zoidal, and, therefore, differ in outline from the description. It may also be distinguished 

 by the ribs, the centenaria being striate. The figure of Mr. Sowerby's duplicata has a 

 close similarity to our shell, but differs in having the 'ribs sulcated along the middle. ' ' ' 

 —Lea, 1833. 



Lea's specimen was young. Shell with a wide sulcus over the umbo to the base, 

 the ribs finest in this sulcus, the anterior and often the posterior ribs divided by a mesial 

 groove; fine ribs alternate with the primary set and sometimes there are three sets 

 formed by the secondary ribs between the large ribs and still smaller ribs rising in the 

 interspaces between these two sets; cardinal area in the larger specimens with eight or 

 nine close-set, v-shaped grooves posterioly, fewer anteriorly; posterior margin of the 



