TRANSACTIONS OF WAGNER 

 1176 



TERTIARY FAUNA OF FLORIDA 



but the typical form is rounded triangular. When quite young it is smooth 

 or merely concentrically striated, but later on develops the prominent con- 

 centric laminae. Occasional specimens are found in which the laminae fail to 

 develop, forming the variety nuda, Dall. 



Aligena pustulosa Dall. 

 PLATE 33, FIGURES 18, 22. 

 Aligena pustulosa Dall, Trans. Wagner Inst., iii., p. 928, pi. 33, fig. 18, 1898. 



Upper Oligocene of the Chipola beds, Chipola River, and of the Alum 

 Bluff sands at Oak Grove, Santa Rosa County, Florida ; Burns. 



Shell small, thin, subtrigonal, moderately inflated, subeqinlateral, with small, 

 pointed, inconspicuous beaks ; valves with a well-marked carina extending 

 downward and forward to the anterior angle of the basal margin, in front of 

 which keel the surface is slightly impressed ; surface sculptured with feeble 

 incremental lines, along which are irregularly distributed small, pointed pustular 

 elevations ; beaks anteriorly twisted with a minute obscure tooth below them on 

 the cardinal margin; ligamentary sulcus long and well marked; scars and 

 pallial line much as in Diplodonta; margin entire, inner surface faintly radially 

 striated. Alt. 6, lat. 5.2, diam. 4 mm. 



The peculiar surface sculpture distinguishes this species at once from the 

 other species. The Chipola specimen is not in very good condition, but shows 

 rather stronger and closer concentric sculpture than the Oak Grove specimens. 



Aligena lineata n. sp. 

 PLATE 44, FIGURE 23. 



Oligocene of the Alum Bluff sands at Oak Grove, Santa Rosa County, 

 Florida ; Burns. 



Shell small, thin, inequilateral, moderately convex, the anterior side longer, 

 rounded, the posterior side higher, shorter, bluntly rounded, the beaks rather 

 elevated, the base evenly arcuate; sculpture of fine, rather irregular elevated 

 lines, not developed into laminae, stronger near the anterior slope and feebler 

 near the posterior slope ; hinge and other characters of the interior much as in 

 the last species. Alt. 7, lat. 8, diam. 4 mm. 



This species is distinguished by its more elongated form and less elevated 

 concentric sculpture from A. aquata, to which of all the species it is most 

 nearly allied. 



