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I 127 



TERTIARY FAUNA OF FLORIDA 



feeble ; exterior smooth or faintly marked with incremental lines, and, in very 

 perfect specimens, microscopic radiating striae; umbones small, polished, con- 

 spicuous ; dorsal margins of the hinge-plate inflected in the right valve ; 

 hinge-plate strong ; right cardinal stout ; prominent ; left valve with the 

 dorsal margins of the hinge-plate slightly bevelled, cardinal teeth subequal, 

 small. Alt. 4, Ion. 4.5, diain. i.o mm. 



This is a peculiar little shell whose rounded form does not suggest the 

 genus, but it has the typical hinge. The radial striae are extremely fine and 

 visible only under magnification in perfect specimens. 



Sportella unicarinata n. sp. 

 PLATE 44, FIGURE 13. 



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



Shell small, solid, compressed, ovate, with the anterior part somewhat more 

 produced and attenuated, interior polished, scars distinct ; exterior divided into 

 two areas by a single sharply defined small thread extending obliquely from 

 the beak to the posterior part of the base, the area behind the thread depressed, 

 surface smooth or faintly microscopically radially striate, with faint irregu- 

 larly distributed incremental lines ; nepionic shell smooth, conspicuous ; hinge 

 normal, the hinge-plate thickened in front of the conspicuous right cardinal 

 tooth ; left cardinals unequal, the anterior most elevated, the left hinge-plate 

 with the posterior dorsal margin slightly inflected. Alt. 4, Ion. 5.5, diam. 1.5 

 mm. 



This species is notable for its depressed posterior areas, which distinguish 

 it from any of our other species. It and the following were found with S. 

 obolus. 



? Sportella lubrica n. sp. 

 PLATE 44, FIGURE 9. 



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



Shell small, thin, polished, ovate-trigonal, sculptured only by incremental 

 lines, which are feeble generally but at intervals strong ; beak low, decurved ; 

 hinge-plate narrow, right cardinal slender, prominent, with a small prominent 

 callus in front of it on the dorsal margin ; shell moderately convex. Alt. 4, 

 Ion. 5, diam. 2 mm. 



A single right valve, somewhat broken, is all that is known of this species. 

 It has not exactly the aspect of Sportella, though nearest to that genus, to 

 which until more material is received it is provisionally referred. 



