PaLARONTOGRAPHICA AjMHRICANA 



"This species is distinguishable at once from the A. ocddentalis of the same size by 

 its uniformly more delicate and much more numerous ribs, and by its greater length in 

 proportion to its height. It is also usually less alate behind and of more uniform, un- 

 distorted shape. Differences of form and proportion seem to separate it sufficiently 

 from A. subprotrada Heilprin * * *" — Dull, 1898. 



Dime7isio7is.— '$,miiX\ valve, Ion. +4,-11; alt. + 1,-5. 5; semidiam, 3 mm. 



Occurrence. — Oligocene of the Chipola beds on the Chipola River, and of the lower 

 bed at Alum Bluff, Calhoun County, Florida. — Dall. Oligocene of Bailey's Ferry, Flor- 

 ida, and Pliocene of the Croatan beds of North Carolina. — C. U. Museum. 



Area occidentalis Philippi 



Plate I, Figures 8, 9, 10, 11 



Area occidentalis Phil., Abbild. u. Beschr., 3, p. 14, pi. 17b, fig. 43-0, 1847. 

 Area zebra Swainson, Zool. 111., No. 26, pi. 118, 1831; ex parta. 

 Area noa of many authors, not of Linne, 



Dall has separated the east American form from the Mediterranean A. 7tocev;\X\\ the 

 above synonj'my. 



Shell oblong, inflated; hinge line as long or nearly as long as the shell; posterior 

 end emarginate; ventral margin with an opening for the byssus; ribs numerous, smaller 

 in the depression opposite the byssal opening, interspaces with from one to several fine 

 riblets; along the posterior cardinal margin and the umbonal ridge radiating strips 

 which are smooth or show only fine riblets; the depression between these smooth ridges 

 with a few normal ribs; beaks small and pointed, little curved; cardinal area wide, flatly 

 concave, ligament area with disconnected diagonal grooves; hinge straight, narrow, 

 with numerous fine, vertical teeth; inner margin practically smooth; color white or yel- 

 lowish with zigzag markings of reddish brown. 



Dimensions. — Lon. + 18,-50; alt. +5,-25; diam. 30mm. 



Occur?-ence. — Oligocene of the Bowden beds, Jamaica; Miocene (?) of Curacao; Pli- 

 ocene of the Caloosahatchie marls, Florida; Pleistocene of the Florida Keys, Yucatan 

 and most of the West Indian Islands; recent in the Antilles generally, and along the 

 eastern coast of the United States northward to the vicinity of Cape Hatteras, North 

 Carolina. — Dall. Recent from Florida and the West Indies. — C. U. Museum. 



Area umbonata Lamarck 

 Plate I, Figures 12, 13, 14, 15, 16, 17 



Area jtDibonata Lamarck, An. s. vert, vol. 6, p. 37, 1819. 

 Area imbricala of several authors. 



Area u>iiho>iata Arango. Kauna Malacologica Cubana, p. 261, 1S79. 



Arco umbonata Dall, Wagner Free Inst. Sci., Trans., vol, 3, pt. 4, pp. 620, 659. 1898; pt. 5, pi. 38, 

 figs. 4, 4a, 1900 



"A testa transversim oblonga, ventricosa; angulato-sinuata; decussatim substriata; 

 umbonibus magnis, arcuatis: latere postico brevi-ssimo. 



