TRANSACTIONS OF WAGNER 



I ;o8 



TERTIARY FAUNA OF FLORIDA 



elevated, concentric lamellae, slightly produced at their intersections with the 

 posterior dorsal keels, the interspaces slightly striated by lines of growth with- 

 out radial sculpture ; hinge with three cardinals in each valve, the posterior 

 right and middle left grooved or bifid ; the rugose area narrow and incon- 

 spicuous but definitely present ; pallial line with a short angular sinus ; the 

 inner border of the valves finely crenate. Height of a short and an elongate 

 specimen respectively 32.5 and 34.0, length 34.0 and 40.0, diameter 22.0 and 

 20.0 mm. ; concentric lamellae 6 to 14 on a radial centimetre. 



This small species appears fully adult and differs from the joung of V. 

 Langdoni in its more numerous, less prominent, and thinner lamellae, which are 

 not bent down and broadened on the posterior slope ; the shell is also less 

 trigonal. From an examination of numerous valves it appears to have much 

 such a series of mutations in form as the larger species, though less pronounced. 

 There seems to be no tendency to effacement of the lamellae in the middle of 

 the disk. It may be regarded as one of the precursors of the large species of 

 the Miocene. 



Venus Langdoni Dall. 



Plate 42, Figures 2, 7, 12. 



l/enus Langdoni Dall, Trans. Wagner Inst., iii., part v., p. 1198, pi. xlii., figs. 2, 7, 12, 1900. 



Oligocene of the Chipola formation at Alum Bluff, Calhoun County, 

 Florida ; Dall and Burns. 



Shell of moderate size, subtrigonal, inflated, with prominent decurved 

 beaks and a large cordate lunule ; posterior dorsal area large, laterally keeled, 

 with coarse concentric striation, the dorsal margin of the right valve somewhat 

 overlapping that of the left; scrdpture of numeroLis rather distant, thick, ele- 

 vated, concentric recurved ribs, which on the posterior part of the disk are bent 

 downward and expanded ; the interspaces are closely, sharply, deeply, concen- 

 trically striated, so that the interspaces of the strije are almost lamellose ; owing 

 to the general slight decortication the internal radial structure of the shell is 

 usually more or less visible, though in a perfectly intact specimen it would be 

 completely hidden; hinge as in the other species, the rugose area in the adult 

 large and prominent ; pallial line with a short angular sinus ; the inner anterior 

 and basal margins of the valves finely crenulate. Height 70, length 88, 

 diameter 50 mm. 



This fine species is named in honor of D. W. Langdon, Jr., who has done 

 much work on our Southern Tertiary. 



The species is distinguished by its heavy, prominent, recurved concentric 



