48 Palaeontographica Americana 48 



the length of the hinge margin; extremities of the hinge margin angulated; anterior 

 ed^e, superior moiety rectilinear; posterior edge rounded; inferior edge nearly rectilinear, 

 or very obtusely rounded; on the hinge space one or two an.gulated lines are drawn from 

 the apex, diverging to the hinge edge * * *."—Say, 1822. 



The name tratisvcrsa arose from the fact that Say interchanged length and height and 

 anterior and posterior. 



Shell inequivalve; ribs thirty to thirty-five, those on the left valve entire, high, nar- 

 row, rounded and irregularly nodvilous, those on the right valve broader and flatter anter- 

 ior to the umbonal ridge; beaks mesially sulcate; cardinal area narrow with two or three 

 V-shaped grooves; posterior margin of the cardinal area elevated; hinge narrow; teeth 

 fine at the center, longer and more oblique distally where the ends of the series curve 

 downward; anterior margin rounded, basal margin rounded or nearly straight, posterior 

 margin rounded below, nearly straight above with an angle at the hinge; inner marinn 

 fluted; epidermis brown. 



A. transversa var. biisatia Harris, (Bull. Am. Pal., vol. i, no. 3, p. 6, 1895), is from 

 the Deep Well of Galveston, Texas. It is longer and less inflated than the usual form. 



Shells from the Pleistocene of New Orleans, Louisiana, are larger and more irregular 

 than the recent trayisversa, but are not so large as shells of this group from the Wacca- 

 maw beds of South Carolina which have been placed under A. plicatura. 



A. transversa Portlock was renamed A. Portlocki by Deshayes. It has been placed 

 in Ctenodonta. 



Dimensio7is. — Lon. +8,-17; alt. +2. 5, -15; diam. 14 mm. 



Occurrence. — Pliocene of Myakka River and De Land, Florida; Pleistocene of North 

 Creek, Little Sarasota Bay, Florida; of Simmons Bluff, South Carolina, Wailes Bluff, 

 Maryland, and Sconset, Rhode Island. Recent from Cape Cod south to Key West, Flor- 

 ida, and southwest to Vera Cruz and the Gulf of Campeachy, Mexico, in shallow water. 

 * * * It is not known below the Upper Pliocene. — Dall. Pleistocene from New Orleans, 

 Chenier, Knapp's Wells, GjTnnasium Well and Lj'dia, Louisiana, and of Wailes Bluff, 

 Maryland; recent from Cameron and Point-au-Fer, Louisiana, Galveston, Texas, Ft. 

 Barrance, Florida, and from Aspinwall. — C. U. Museum. 



Area triphera Dall 

 Plate XI, Figure 7 



Scapharca {Scapharca) triphera Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 648, pi. 33, 

 fig. 6, 1898. 



"Shell subequivalve, of moderate size, elongate, not much inflated, subrectangular, 

 with low beaks slightly prosoca:lous and marked by a conspicuous wide mesial sulcation ; 

 tmibones situated at the anterior third of the length; left valve with about thirty-eight 

 rounded subequal ribs separated by narrower interspaces; in the adult about a dozen of 

 the anterior ribs may be squared off and deeply mesially sulcate near the margin, while a 

 few of the ribs on the posterior dorsal slope are narrower, smoother, and more widely sep- 

 arated; transverse sculpture of elevated lines which are somewhat regularly spaced, and 



