S4 



Pat-akontographica Americana 54 



Dimaisions. — Lon. + 15,-31; alt.+6,-24; diain. 32 mm. 



Ocairrence. — Chesapeake Miocene of Alum Bluff, Calhoun County, Florida. — Dalt. 

 Miocene of the Upper bed at Alum Bluff, Florida. — C. U. A/useum. 



Area campsa Dall 



Plate XII, Figure 12; Plate XIII, Figures, i, 2, 3 



Scapharca {Anadara)campsa Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 656, pi. 32, fig. 

 ii, 1898. 



"Shell of moderate size, solid, and heavy, with a straight and angulate upper margin, 

 obliquely rounded anterior, produced posterior, and arcuate basal margin; beaks low, 

 much incurved, mesially impressed, and rather anterior; left valve with about twenty- 

 two narrow ribs separated by wider interspaces, crossed by little elevated, regularly 

 spaced incremental lines; the ribs are not nodulous, the anterior ones are flattish or 

 rarely have a shallow sulcus mesially near the margin; they are subequal, but in speci- 

 mens in which the mesial depression of the valve is especiallj' strong, the ribs included 

 in it are narrower and closer together than usual; hinge-line nearly as long as the shell, 

 angular, but not auriculate distally; the beaks are within the anterior third; cardinal 

 area wider in front, narrow behind, longitudinally striated with a few grooves which cir- 

 cumscribe a 'stemmed' arrow-head figure, few of them reaching as far forward as the 

 beaks; teeth in two adjacent series, the anterior shorter with a pronounced thickening of 

 the shell below it, over the vertical face of which the teeth extend rather irregularly or 

 are supplemented by denticular ^vrinkles; posterior series longer, numerous, vertical, dis- 

 tally much wider, and more or less obUque; interior margin of the valves with strong, 

 short flutings. Lon. 47; alt. 28; diam. 27 mm. 



"This is quite a peculiar species, the teeth of which recall .4 ;y/«(7, while all the other 

 characters of the shell indicate its section to be Anadara, another instance, if one were 

 needed, to illustrate the mutability of the dental forms in this family. It cannot be con- 

 founded with any of our other species." — Dall, 1898. 



Ribs twenty-one or twent}'-two; cardinal area with margin elevated behind the 

 beaks ; the mesial sulcation of the beaks passing over the umbo and down to the ventral 

 margin as a broad flattening or sulcation. This shell is distinguished by its wide, 

 rounded interspaces and narrow, square-topped ribs crossed by elevated lines as in .4. 

 arcsta and by its mesial depression. In a pair of valves which belong together this de- 

 pression is more marked on the left valve. 



Dimensions,. — -Lon. + 16,-36: alt. +6,-25; diam. 29 mm. Dimensions of a large 

 valve, lon. 64, alt. 43 mm. 



Ocrurnnce. — Chesapeake Miocene or upper bed at Alum Bluff, Florida. — Dall. Mi- 

 ocene of the upper bed at Alum Bluff", Florida. — C. U. Museum. Dr. Maury lists this 

 species from the Oligocene of Alvim Bluff, hut the specimens listed prove to have come 

 from the upper bed. 



