38 Paleaontographica Americana 38 



The ornamentation of this species closely resembles that of A. subrostrata. The 

 interspaces are narrower in A. dodona. Otherwise the two species are distinct. In A. 

 siibrostrala the posterior part is not so attenuate, the hinge is proportionately shorter, 

 even in the largest specimens of A. dodotia there is no gap in the hinge teeth as in the 

 older specimens of A. stibrostrata and the posterior margin of A. dodona makes a decided 

 angle with the hinge-line, which is not the case in A. stibrostrata. In general form A. 

 dodona resembles A. santarosaiia, but it is proportionately longer and the ribbing is 

 different. 



Dimensions. — L,on. + i7,-34; alt. + 7,-27; diani. 35 mm. This is an unusually large 

 specimen. 



Occurrence. — Oligocene marl of Oak Grove, Santa Rosa County, Florida. — Dall. 

 Oligocene of Oak Grove, Florida. — C. U. Museum. 



Area santarosana Dall 

 Plate IX, Figures i, 2, 3 



Scapliarca {Scapliarca) santarosana Dall, Wagner Free lust. Sci.. Trans., vol. 3, pt. 4, pp. 641, 642, 



pi. 31, figs. 2, 10, 1S9S. 

 Area [Scap/iarca) santarosana Waurj', Bull. Aui. Tal., vol. 3, p. 375, 1902. 



"Shell small, short, plimip, rostrate, with moderately elevated, mesially sulcate pros- 

 occelous beaks; left valve with thirty elevated, squarish, radial ribs, separated by slightly 

 narrower channelled interspaces; the ribs on the posterior slope are low, smaller, and 

 nearly smooth; those on the middle of the shell have mostly near the margin a shallow 

 mesial sulcus; in those still more anterior the sulcus is deeper and wider, dividing each 

 rib over most of its length into two more or less rounded riblets; concentric sculpture of 

 regularly spaced elevated lines, which on the ribs appear as prominent ripples; right valve 

 having the ribs narrower and less strongly sculptured, and the sulci less distinct ; cardinal 

 area short, with about three concentric grooves; beaks within the anterior fourth; hinge- 

 line short, with about fifty-seven rather irregular, closely adjacent, nearly vertical teeth, 

 longer and more oblique distally; margins strongly fluted; base flexuous, posterior end 

 narrow, pointed, without any marked angle at the end of the hinge-line. Lon. 36.5, alt. 

 28, diam. 28 mm. 



"This species is most nearly related to A. staminata Dall, from which it can be dis- 

 tinguished especially by its lower beaks, more oblique posterior slope, more flexuous base, 

 and attenuated posterior end." — Dall, 1898. 



Ribs twenty-eight to thirty- two; some of the specimens from Bailey's Ferry are short 



■ and have a wide cardinal area with many grooves. The beaks are more anterior and 



more sulcate than in A. staminata. This species somewhat resembles a variety of A. 



staminea from Patuxent River, Maryland, but the latter is less nodulous on the central 



and anterior portions and the ribs on the umbonal ridge are striated. 



Dimensions. — Lon. -1-9,-24; alt. -1-7,-20; semidiam. 14 mm. 



Occurrence. — Oligocene of the Chipola River marl, of the lower bed at Alum Bluff, 



