TRANSACTIONS OF WAGNER 

 622 



TERTIARY FAUNA OF FLORIDA 



apices slightly prosogyrate, cardinal area long, narrow, lozenge-shaped, flattish, 

 with longitudinal stria;, the site of the resilium marked on each valve by two 

 grooves forming a small triangle, within which are traces of the inception of 

 other grooves; sculpture chiefly of fine radial riblets overrunning and some- 

 what imbricated by not prominent lines of growth ; the radials which end on 

 the margin of the byssal foramen are perceptibly finer than the rest, those 

 on the posterior dorsal slope are more or less fasciculated, the ends of the 

 fascicles dentating the posterior margin ; on the dorsal anterior part the riblets 

 increase somewhat in size, but are not fasciculated ; the dorsal border in front 

 is anterior to the rest of the margin ; between the dorsal posterior extreme and 

 the ventral posterior angle there is often an irregular but not deep emargina- 

 tion ; the borders of the byssal foramen are irregularly emarginate ; interior 

 smooth, the margin denticulated by the sculpture except at the foramen ; 

 hinge-line straight, minutely denticulate ; the teeth in the centre smaller, those 

 towards the ends inclined outward slightly, above, and a little larger; there 

 are about twenty-three anterior and forty posterior teeth, with no marked 

 hiatus between the series. Lon. of shell 28, alt. of hinge-line 8.5, of beaks 

 IO, diam. at the umbonal part IO mm. It is quite possible that the shell 

 grows to a considerably larger size. 



This species is distinguishable at once from the A. occidentalis 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, undistorted shape. Differences of form and 

 proportion seem to separate it sufficiently from A. subprotracta Heilprin. 



Area halchetigbeensis Harris from the Lignitic or Chickasawan stage is 

 shorter and more finely sculptured, though closely related. 



Area bowdeniana n. s. 

 PLATE 33, FIGURE 12. 



Oligocene of the Bowden beds, Jamaica, and Pliocene of Limon, Costa 

 Rica ; Bland, Henderson, and others. 



Shell small, inflated, somewhat irregular, very inequilateral, the beaks 

 almost posterior ; dorsal slope conspicuous ; its outer border with a stout keel 

 and its surface somewhat excavated ; beaks small, pointed, prosogyrate ; car- 

 dinal area wide, lozenge-shaped, flattish, with a few grooves for the resilium 

 forming a smaller lozenge near the beaks ; sculpture as in A. nnibonata, the 

 imbrications close and subnodulous ; shell not alate in front and with the 



